work on the ontology of coordinate reference systems

[Chris Partridge]

Hi,

We are now revisiting some work on the ontology of coordinate reference systems - and the notion of a ‘spatial object’ - that we started around 15 or so years ago. Now, as we look a little more closely at the details quite a few questions emerge. I’m wondering whether there are people in the community with views on the topic, would be good to hear any thoughts.  

The work is a little technical, so for those without the technical background I will set it up. There is a LOT of material, so I’m going to start setting things up in this first post to see whether anyone is interested. If they are, I can post more.

Plato and Aristotle have a process that starts with the  "τί ἐστι" (ti esti, "what is it?") question - and it seems a good way in here. Overall, we can frame this as trying to understand: what is a Coordinate Reference System (CRS).

Coordinate points are key components of Coordinate Reference Systems (CRSs). So, let’s start small and ask what a single coordinate point is. It’s always good to start with an example, so let’s use ‘Null Island’ (http://en.wikipedia.org/wiki/Null_Island - “the location at zero degrees latitude and zero degrees longitude (0°N 0°E), i.e., where the prime meridian and the equator intersect.”). Let’s link this to a specific CRS - WGS 84 (G1150 - 7661) (https://epsg.io/7661 - an Ellipsoidal 3D Coordinate system CRS).

We often think of a coordinate point as a fixed point in space. But what is characteristic about this Null Island coordinate point specifically, and coordinate points in general, is that it/they remain at the same place over time (in the sense of the same position in the coordinate system). So, Null Island is in the same place (in this sense) today, tomorrow and next week.  From this perspective, it is time invariant, at every time it is in the same place. All coordinate points (in a CRS) are similarly time invariant - at every time in the same place relative to each other.

If one now takes a four-dimensional spacetime perspective, then the coordinate point places at each time can be taken together and fused into a trajectory over time. In relativity, this is known as a worldline (https://en.wikipedia.org/wiki/World_line - “The world line (or worldline) of an object is the path that an object traces in 4-dimensional spacetime.”) So Null Island is (from a spacetime perspective) the worldline that is at 0°N 0°E at each point in time.

All the coordinate points in the WGS 84 (G1150 - 7661) CRS are also (from a spacetime perspective) worldlines. And this family of worldlines (belonging to the CRS) do not intersect and cover the relevant portion of spacetime (as every point in the bit of spacetime the coordinate system covers has a (different) coordinate point.) This is a well-known feature in relativity (physics), where it is called a congruence. More specifically, the CRS's set of coordinate point worldlines are called a timelike congruence (https://en.wikipedia.org/wiki/Congruence_(general_relativity)) as the worldlines are (by definition) timelike. (see https://plato.stanford.edu/entries/spacetime-iframes/#InerFramNewtSpac)

In general, a CRS is built using a geodetic datum where a geodetic datum is (according to Wikipedia - https://en.wikipedia.org/wiki/Geodetic_datum) a global datum reference or reference frame for unambiguously representing the position of locations on Earth by means of either geodetic coordinates (and related vertical coordinates) or geocentric coordinates. So the datum fixes the coordinate point worldlines and so the timelike congruence.

Specifically, The CRS WGS 84 (G1150 - 7661) is based upon the World Geodetic System 1984 (G1150) datum (https://epsg.io/1154-datum). Other CRSs are based upon this datum - for example: WGS 84 (G1150 - 9055) (https://epsg.io/9055 - an Ellipsoidal 2D Coordinate system CRS); and WGS 84 (G1150 - 7660) (https://epsg.io/7660 - a Cartesian 3D CRS) also use this datum. And so the coordinate points for each of the CRSs pick out the same family of worldlines, the same timelike congruence.

What is also interesting is that the actual coordinates values can differ - the ellipsoidal CRSs are 3D <(0, 0, 0)> and 2D <(0, 0)> - and the Cartesian is <(6378137.000, 0, 0)> - but these all label the same worldline. It is recognised that - and this example shows - that while the timelike congruence is an essential component of the CRS, it is not sufficient to uniquely pick out a particular CRS - see e.g. Nerlich or Norton in these notes (https://en.wikipedia.org/wiki/Frame_of_reference#Notes).

As this also implies, different geodetic datum will differently represent the position of locations on Earth. More specifically, different datums will lead to different Null Islands. So the datum World Geodetic System 1984 (G1674 - 1155)(https://epsg.io/1155-datum) will have a different timelike congruence - and so a different Null Island - 0°N 0°E in its ellipsoidal system - and, in some cases, evolve differently over time (due to, for example, different velocity models. Though these differences may be quite small.

Hopefully you can begin to see now how worldlines and congruences are a natural way to start understanding coordinate systems. Indeed, the above picture can be seen as a physicalization of the topology and geometry that should be familiar from the relativity literature - and its talk of coordinate systems. In this there is much talk of materialising - physicalising the geometry (and topology). There have been a number of ways to describe how this materialises. Einstein talked about a reference mollusc. People also talk about a fleet of clock-carrying particles or perfect fluids or dust or incoherent dust. However, the picture does rely on Einsteinian relativity - it applies equally well to Galilean relativity over Newtonian/Euclidean space-time. It is more about the general structure of spacetime than any specific physical theory (see e.g. Stein, H., 1967, “Newtonian space-time”).

From a more mathematical (topological) perspective, the shift from spacetime to the timelike congruence can be seen as making a quotient space, where the worldlines are the ‘points’ of the new space. If one assumes (as is usually done) the spacetime has a classical mereology. This new space is a ‘spatial’ classical sub-mereology of spacetime. So the standard formalisations of mereotopology (e.g. RCC and Egonhofer) work in this space. This space can be seen as providing a common spatial basis for a set of CRSs - where the mereotopological relations hold across these spaces (and break down when applied to CRSs outside the space, unless they are restricted to a particular specific time).

Something odd appeared in our literature survey though. The relativity literature has extensive discussion of coordinate systems, worldlines and congruences - with links to differential geometry. But the geodesy and geospatial literature has very little - apart from relativistic geodesy, where I guess there is little choice but to engage. Though talk about station positions and velocities gets very close to the notion of congruences. I wonder why this is so. One could hypothesise that as most of the grounding work in geodesy was done in the 18th and 19th centuries, there has been no pressure in the community to take on the ideas in relativity.

Whatever the reason, it seems odd, as the notions of worldlines and congruences seem a natural conceptual framing for coordinate systems. For example, congruences naturally capture the extent of the underlying spatial mereotopology. They also suggest easy ways to formalise using mereotopology. Is there some other underlying reason for this lack of uptake?

[Barry Smith]

you might try asking Alan Ruttenberg -- he has thought about this -- it is truly a gap in BFO support documents, since sites and spatial regions are distinguished, in BFO, by the fact that the latter is determined relative to a frame of reference

did someone give you (4-dimensionists) permission to deal with spatial locations?

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[Ravi Sharma]

Chris

i started reading and saw violations of space and time hence did not go further zero island has to be either between two or more points on earth or inertial if time inveriant

either you are talking of inertial reference or Earth reference

you need to clarify that

for Earth NASA Google and now AI? may help

for inertial we have probes managing beyond solar system and astrophysics almost to end of physical universe

space time comes into picture only shen you consider relativity

another math and geometry reeuire hou to define Euclid Hilbert affine rtc

I know you know some of this a lot as veteran researcher so why ? is there some new?

regards

Thanks.

Ravi

(Dr. Ravi Sharma, Ph.D. USA)

NASA Apollo Achievement Award

​Former Scientific Secretary iSRO HQ

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[Ravi Sharma]

Chris on further reading, I see that you are referring to mereotopology and yes looking at mathematical point and I am studying the Skyrmion type particles related topology 

So can You all and Berry respond to my related Q 

while physics will almost always deal with finites even at infinitesimal scales mathematical point does not have to obey Planck type limts

therefore is there a case for ontology of these two together?

Regards yes you are in depth but why do you need null island in earth geodesy?

Thanks.

Ravi

(Dr. Ravi Sharma, Ph.D. USA)

NASA Apollo Achievement Award

​Former Scientific Secretary iSRO HQ

Ontolog Board of Trustees

Particle and Space Physics

Senior Enterprise Architect

SAE Fuel Cell Standards Member

[Neil McNaughton]

>>In general, a CRS is built using a geodetic datum where a geodetic datum is (according to Wikipedia - https://en.wikipedia.org/wiki/Geodetic_datum) a global datum reference or reference frame for unambiguously representing the position of locations on Earth by means of either geodetic coordinates (and related vertical coordinates) or geocentric coordinates.

 

FYI the “datum” business is more complicated than you might imagine. The US National Spatial Reference System is currently being ‘modernized’ as North American Datum (NAD) 83 and vertical datums such as the North American Vertical Datum (NAVD) 88 are to be replaced with new terrestrial reference frames and a novel geopotential datum. The changes are designed to incorporate a ‘dynamic earth’ i.e. with mobile tectonic plates and time-variant datums.

 

Also a good reference for geodesy etc is the European Petroleum Survey Group https://EPSG.org  and its Geodetic Awareness page https://epsg.org/geodetic_awareness.html.

 

My 2 cents… The topic is one for specialists. There is a lot of prior art. Also in my humble opinion, RDF is a poor tool for science and engineering. Modeling with RDF quickly becomes idiosyncratic and unintelligible to the domain specialist. Perhaps this is the intent?

 

I nonetheless very keen to hear of examples of successful RDF modeling in a scientific context.

 

Best regards,

Neil McNaughton

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My 2 cents

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[Chris Partridge]

Hi Barry,

Do we need permission?

It would be good if Alan took a look.

This (as you know from our discussions)  is building upon prior work. 

Chris

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[Chris Partridge]

Hi Ravi,

There is a detailed geodesy aspect to the topic (and a relativity one), that I am hoping doesn't need to be gone into.

While "Skyrmion type particles related topology" and e.g. 'causal set theory' are extremely interesting. I'm working in the space of coordinate systems. And I'm hoping that we can abstract away from these technical matters for this perspective. What would be interesting is if topics such as "Skyrmion type particles related topology" could shed light on this more general topic. Be good if you could point us to something along those lines.

This is more about the 'philosophy' (ontology) of space, time and spacetime - and how it can frame discussions in geodesy and geospatial information.

You asked: ... but why do you need null island in earth geodesy?

I was using this as a starting point for the 'ontological' analysis. I was looking for an interesting coordinate point to discuss - and this is what people often choose.

Geodesy uses coordinate systems - Geodesy defines global and regional reference frames like WGS84. These systems contain points. So I thought it would be easiest to start with the points. These have a much simpler structure than the whole system.

Chris

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[Chris Partridge]

Hi Neil,

let me reply inline ...

Chris

On Fri, 6 Feb 2026 at 08:48, Neil McNaughton <nei...@oilit.com> wrote:

>>In general, a CRS is built using a geodetic datum where a geodetic datum is (according to Wikipedia - https://en.wikipedia.org/wiki/Geodetic_datum) a global datum reference or reference frame for unambiguously representing the position of locations on Earth by means of either geodetic coordinates (and related vertical coordinates) or geocentric coordinates.

 

FYI the “datum” business is more complicated than you might imagine. The US National Spatial Reference System is currently being ‘modernized’ as North American Datum (NAD) 83 and vertical datums such as the North American Vertical Datum (NAVD) 88 are to be replaced with new terrestrial reference frames and a novel geopotential datum. The changes are designed to incorporate a ‘dynamic earth’ i.e. with mobile tectonic plates and time-variant datums.

 

Yes, the geodesy quickly gets complicated, so the idea here is to rise above this and look at the general mereotopology and geometry.

 

Also a good reference for geodesy etc is the European Petroleum Survey Group https://EPSG.org  and its Geodetic Awareness page https://epsg.org/geodetic_awareness.html.

The ISO (if you can get hold of them) and OGC standards are useful too. (For transparency, note I am a member of the UK's ISO  IST/36 - Geographic information committee)

 

My 2 cents… The topic is one for specialists. There is a lot of prior art. Also in my humble opinion, RDF is a poor tool for science and engineering. Modeling with RDF quickly becomes idiosyncratic and unintelligible to the domain specialist. Perhaps this is the intent?

Umm, I think there is a topic for our community in how space, time and spacetime work together. As far as I can tell, this is to some extent orthogonal to the geodesy and relativity details.

There is a lot of literature on this topic in various areas, including the philosophy of space and time, which has close links to relativity.

There seems to be a lot less in geodesy and geospatial information.

It is acknowledged as an issue in e.g the ISO standards: the Introduction of ISO 19108:2002 says: “Behaviour in time may be described more easily if the temporal dimension is combined with the spatial dimensions, so that a feature can be represented as a spatiotemporal object. … This International Standard has been prepared in order to standardize the use of time in feature attributes. Although it does not describe feature geometry in terms of a combination of spatial and temporal coordinates, it has been written to establish a basis for doing so in a future standard within the ISO 19100 series.” There is also a link noting Einstein's relative space in the same standard.

If you wish, I can point to other sources that acknowledge this as a known issue.

This is, as I said, an area I have been working on for a while. See, for example, some of my geospatial reference systems papers

• Partridge, C. (2011). An Information Model for Geospatial and Temporal References. https://www.academia.edu/39988229
• Partridge, C. (2013). Geospatial and Temporal Reference – A Case Study Illustrating (Radical) Refactoring. ONTOBRAS-2013 6th Ontology Research Seminar in Brazil. https://www.academia.edu/27433806/
• Partridge, C., Mitchell, A., Loneragan, M., Atkinson, H., de Cesare, S., & Khan, M. (2019). Coordinate Systems: Level Ascending Ontological Options. 2019 ACM/IEEE 22nd International Conference on Model Driven Engineering Languages and Systems Companion (MODELS-C), 78–87. https://www.academia.edu/40354620
• Partridge, C., Mitchell, A., Loneragan, M., Atkinson, H., de Cesare, S., & Khan, M. A. (2020). The Fantastic Combinations and Permutations of Coordinate Systems’ Characterising Options. The Game of Constructional Ontology. https://www.academia.edu/118060077/

 

I nonetheless very keen to hear of examples of successful RDF modeling in a scientific context.

I'm not sure what this has to do with RDF. 

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[Joshua Lieberman]

Hi Chris, et al,

There is active work on a CRS ontology by OGC and W3C groups based on the standards and models from both OGC and ISO TC211. https://github.com/opengeospatial/ontology-crs

There is also an important omission in Chris’ exposition, which is “object”. The geocentric CRS models (and geodetic framework on which they rest, are intended to locate objects on the earth’s (or other planetary bodies’) surface using coordinates. This is an important consideration when thinking about coordinate reference systems because there is nothing static or eternally persistent about the earth’s surface. Geodetic datums are dated not just for historical interest. The high-resolution ones are updated yearly in order to maintain sufficient accuracy with regard to object locations in the face of continental drift and other tectonic forces. Yes, it’s complicated, but for good reason when the real world (or an accurate virtual representation) is involved.

—Josh Lieberman

On Feb 6, 2026, at 4:36 AM, Chris Partridge <partri...@gmail.com> wrote:



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[Sandro Rama Fiorini]

Hello Chris! We published and standardized some work on that topic a long time ago. Our take was much simpler than what you are describing, but it might interest you nonetheless:

- Paper: https://ieeexplore.ieee.org/abstract/document/6696603

- IEEE 1872: https://ieeexplore.ieee.org/document/7084073

best,

Sandro

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[Alex Shkotin]

Chris,

Examining the definitions of various coordinate systems in various sciences and technologies is a large and painstaking undertaking.

I can only share an application of Hilbert's "coordinate system" approach in Foundations of Geometry.

In my own words, but as close to Hilbert's ideas as possible:

A coordinate system in space, for example on a plane, is a figure consisting of two perpendicular lines, on each of which a point distinct from the intersection point (called the origin and usually denoted by O) is chosen and uniquely named. The traditional names for one of the points are X and for the other, Y. The lines on which they are located are called the X- and Y-axes, respectively. The corresponding rays O-X and O-Y are called the regions of positive coordinates, respectively, the X- and Y-axes.

The segments O-X and O-Y are considered unit segments of their axes and are usually equal in length. Any point on the plane is uniquely associated with its X coordinate: a segment or point labeled X. The segment must also have an attribute: a sign with the values "+" or "-" depending on which direction from O it should be placed: "+" toward X, "-" toward the opposite direction. The same applies to Y.

Thus, to present coordinates, one must specify a pair of correctly attributed segments and points somewhere, perhaps on another plane parallel to the given one.

Hilbert's originality lies in the fact that he doesn't operate with non-geometric entities—real numbers.

Which requires a separate transition.

So, for Hilbert, a coordinate system is a labeled figure like this one.

It would be interesting to gather definitions from various theories and technologies in one place. I'd like to participate.

Alex 

чт, 5 февр. 2026 г. в 20:51, Chris Partridge <partri...@gmail.com>:

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[Chris Partridge]

Hi Alex,

In the context of GeoSpatial systems it is an interesting question what a coordinate reference system is.

https://en.wikipedia.org/wiki/Spatial_reference_system --- A spatial reference system (SRS) or coordinate reference system (CRS) is a framework used to precisely measure locations on, or relative to, the surface of Earth as coordinates. It is thus the application of the abstract mathematics of coordinate systems and analytic geometry to geographic space. A particular SRS specification (for example, "Universal Transverse Mercator WGS 84 Zone 16N") comprises a choice of Earth ellipsoid, horizontal datum, map projection (except in the geographic coordinate system), origin point, and unit of measure. Thousands of coordinate systems have been specified for use around the world or in specific regions and for various purposes, necessitating transformations between different SRS.

While making no claims for the accuracy of the Wiki description, it is broadly correct that "It is thus the application of the abstract mathematics of coordinate systems and analytic geometry to geographic space."

As the earlier example of Null Island shows, a coordinate point in a coordinate reference system is something more than one in a Hilbert geometry. (BTW I admire Hilbert's geometry)

One also probably needs both a little more and a little less structure to replicate the multiple timelike congruences that underlie the multiple coordinate reference systems.

Best,

Chris

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[Chris Partridge]

Hi Josh,

Excellent link!! (also click through to https://www.w3.org/groups/wg/sdw/ - Spatio-temporal Data on the Web Working Group) --- Admirable goal: "The ultimate goal is to attain a web ontology for coordinate reference systems (CRS), approved both by the OGC and the W3C."

WRT: "There is also an important omission in Chris’ exposition, which is “object”. The geocentric CRS models (and geodetic framework on which they rest, are intended to locate objects on the earth’s (or other planetary bodies’) surface using coordinates."

Yes, absolutely. This is one of the justification for having coordinate reference systems.

From a methodological perspective. As I said in the original post, for clearing up ontological matters, I am following a plan that starts small and expands out. We have been working on this relation already - and at some stage in the exposition we need to discuss it. So more of a later treat than an omission. 

I see this site ( https://github.com/opengeospatial/ontology-crs) inherits some ISO definitions: 

coordinate system: A coordinate system is a set of mathematical rules for specifying how coordinates are to be assigned to points.

coordinate reference system: A coordinate reference system (CRS) is a coordinate system that is related to an object by a datum.

datum: A datum is a parameter or set of parameters that define the position of the origin, the scale, and the orientation of a coordinate system.

https://isotc211.geolexica.org/concepts/93/ - coordinate system
set of mathematical rules for specifying how coordinates are to be assigned to points
[SOURCE: ISO 19111:2019]

https://isotc211.geolexica.org/concepts/703/ - coordinate reference system
coordinate system that is related to an object by a datum
Note to entry: For geodetic and vertical datums, the object will be the Earth.
[SOURCE: ISO 19111:2019]

I am hoping to get some clarity, as I said at the beginning of my post, on the "τί ἐστι" (ti esti, "what is it?") question applied to points in the definition above.

I have found some definitions that might get us started: 

https://isotc211.geolexica.org/concepts/1166/ - geographic point location
well defined geographic place described by one coordinate tuple
[SOURCE: ISO 19145:2013]

https://isotc211.geolexica.org/concepts/1167/ - geographic point location representation
syntactic description of a geographic point location in a well known format
[SOURCE: ISO 19145:2013]

also ...

https://isotc211.geolexica.org/concepts/347/ - position
data type that describes a point or geometry potentially occupied by an object or person
Note to entry: A direct position is a semantic subtype of position. Direct positions as described can only define a point and therefore not all positions can be represented by a direct position. That is consistent with the "is type of" relation. An 19107 geometry is also a position, just not a direct position.
[SOURCE: ISO 19133:2005]

But, as one digs down, one gets the feeling that some prevarication is going on. Especially if one looks at the relativity literature where things are much much clearer.

@josh - if you have any insight into this or related matters, it would be appreciated.

Also, it seems to me that while there is a lot of complicated technical matter here, the relation between space and time is relatively (excuse the pun) straightforward if you bite the bullet and try to make things clear. It is a conceptually cleaner and simpler part of the overall system.

Best,

Chris

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[Ravi Sharma]

Chris

Many thanks for details and references. I went to your most recent reference in your reply in this thread.

It opens my eyes on at least more than 2 or 3 decades of work you have been doing on Business Objects ontology and standards and related research.

I plan to soon revert to see if I can relate to your Null Ontology and your Q. I also plan to sound out particle topologists.

I can see applications already to constellations of multiple LEO and MEO objects and also viewing opportunities from those of a fixed space-time object such as a point tied to time and space on Earth or in these orbits.

As a physicist, not beyond a student, my understanding is that multiple tuples and multipole expansions of basic geoids, replaced by numeric realtime gravitational (geodetic) points on and near earth space depend on realtime values of mundane things like rain and cloudmass movements as well as known anomalies such as Bermuda Triangle related to mass anomalies in earth crust or surface.

Why would these be related or helped by your Null Island abstraction for Earth Geodesy?

I am excluding Math and metaphysical Ontology for the time being not having studied those.

Appreciate your extensive work.

Regards.

Thanks.

Ravi

(Dr. Ravi Sharma, Ph.D. USA)

NASA Apollo Achievement Award

Former Scientific Secretary iSRO HQ

Ontolog Board of Trustees

Particle and Space Physics

Senior Enterprise Architect

SAE Fuel Cell Standards Member

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[Alex Shkotin]

Chris,

The mathematics and physics of WGS 84 are very interesting. I'll have to look into it. I'd start with the South Pole—it's the only place where one of the axes meets solid ground, albeit icy, and it moves 10 meters per year. But they say that even if there were rock at the point where the axis meets solid ground, it would still move. What progress has mathematical usage made!

I would ground mathematical models of spacetime in the corrections of general relativity and special relativity for satellite navigation. But I'm a long way from that.

Best,

Alex

пт, 6 февр. 2026 г. в 20:03, Chris Partridge <partri...@gmail.com>:

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[Mike Peters]

Chris,

This is a great project. I need to use 4D Spacetime in Pipi 10 (the next version). I will read all this with great interest.

I have used a great deal of your and Matthew West's previous work. All excellent. Thank you.

Mike Peters

NZ
https://www.blog.ajabbi.com

[Chris Partridge]

Hi Mike,

Good to hear from you.

Be really useful to hear any experiences you have with geospatial systems in Pipi 9 and 10.

Chris

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[Chris Partridge]

Hi Ravi,

Be really useful if you could find some connections with the more technical areas in physics.

The target is the standard geospatial structures used in the ESPG and PROJ databases (https://proj.org/en/9.3/index.html), but we have found that when building the mereotopology (and geometry) for these that some of the more technical work provides useful scaffolding.

For example, when trying to formalise what a worldline is, the work on causal structures (https://en.wikipedia.org/wiki/Causal_structure) in Lorentzian manifolds by Penrose, Hawking et al gives a useful framework that we can reuse.

Within our scope of "the standard geospatial structures used in the ESPG and PROJ databases" we consume the work done on "mass anomalies on the earth's crust or surface" to fix the coordinate systems, but these are (it seems to me) mostly out of core scope.

Chris

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[Chris Partridge]

Hi Barry,

WRT: "since sites and spatial regions are distinguished, in BFO, by the fact that the latter is determined relative to a frame of reference"

A quick search threw up the superseded document: http://ontology.buffalo.edu/bfo/Reference/old%20versions/BFO_Nov9_noon.pdf

Which says: 

2.1.2.3 Spatial region

We recommend that users of BFO:spatial region specify the coordinate frame which they are

employing, for example, when dealing with spatial regions on the surface of the Earth, the coordinate

frame of latitude and longitude. Such coordinate frames can be associated with a Newtonian or a

relativistic frame of reference. The reference frame might be relative to a moving object such as the

earth, in which case the corresponding spatial regions move with the movement of the earth.

However, they are at rest relative to their coordinate frame. Lines of latitude and longitude are two dimensional object boundaries which can move; however, they are by definition at rest relative to the

coordinate frame which they determine.

Elucidation: A spatial region is, intuitively, a 0-, 1-, 2- or 3-dimensional part of space. This

elucidation will fall short, however, unless it is understood in a way that conforms with what we

know from the theory of relativity. One step in this direction is to add: a spatial region is the sort of

entity that can be specified by means of a coordinate frame, and is always at rest relative to this

coordinate frame.

Example: The Tropic of Capricorn (with the coordinate frame defined by the lines of latitude and

longitude)

Spatial regions have no qualities except shape, size and relative location.

Object boundaries and sites are distinguished from the spatial region which they occupy at any given

time in the sense that (1) the former move when their material host moves, and they change shape or size when their material host changes shape or size; (2) the latter must be specifiable in terms of some system of coordinates, and they are by definition at rest relative to this coordinate frame.

I'm guessing that this is still a reasonably accurate statement of the position.

Chris

On Thu, 5 Feb 2026 at 19:02, Barry Smith <ifo...@gmail.com> wrote:

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[Chris Partridge]

Hi Sandro,

I noticed this in your paper.

"Such as with time in SUMO, we introduce the notions of position point and position region. A position point refers to a point in a coordinate system projected on the physical space. A position region is an abstract region in a coordinate system overlapping the physical spatial region occupied by the object. Both position point and position region are types of position measurement; i.e., ∀p PMeasure(q) ↔ PPoint(q) ∨ PRegion(q) and ∀q PPoint(q) → ¬PRegion(q). 

Also, it is important to note that all these definitions are synchronic; i.e., they consider only situations like snapshots in time. As such, two objects cannot have the exact same quantitative position; i.e., they can not be located at the same position point.   

Operationally, it is quite clear how this works. The interesting question is what the position point and position region are.

On a first reading, it seems they persist in time as they are used at various different snapshots in time.

My analysis so far would see position points as (4D) wordlines and position regions as (4D) worldtubes. 

This interpretation seems to be consistent with both usage and intention - and give a simple physical (mereological) meaning to the PMeasure predicate. 

Does this work for your intuitions?

Best

Chris

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[Sandro Rama Fiorini]

Hello, Chris.

>  On a first reading, it seems they persist in time as they are used at various different snapshots in time.

Yes, if memory serves me right. Time was not one of our main concerns, so we did not include it explicitely.  

Maybe one could try to achieve some sort of diachronic use of the ontology by means of SUMO's modal axioms (e.g., holdsDuring).

> My analysis so far would see position points as (4D) wordlines and position regions as (4D) worldtubes. 

> This interpretation seems to be consistent with both usage and intention - and give a simple physical (mereological) meaning to the PMeasure predicate. 

> Does this work for your intuitions?

It makes sense to me. At the very end of the conclusion we mentioned something like that as a possible extension, so probably some of us were already thinking in that direction. 

However, what you are doing seems much more sophisticated, especially if you take relativity into account. I am not sure that we could make POS compatible with relativity, even though we did not assume a universal reference frame,

best,

Sandro

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[Chris Partridge]

Hi,

WRT: Maybe one could try to achieve some sort of diachronic use of the ontology by means of SUMO's modal axioms (e.g., holdsDuring).

Exactly. This is the nub of the challenge. Working out the nature of and the tradeoffs on the holdsDuring for the general case. You can see these in action when you look at the spatial embedding of coordinate reference systems. Of course, you can simplify things for local cases.

Chris

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[Mike Peters]

Hi Chris

I have been thinking about how to proceed. These are some initial ideas specific to Pipi 9 and 10.

A couple of years ago, when Matthew was still alive, I did a deep dive into your book, talks and papers, and all those of Matthew I could find. Especially BORO, NATO, Shell Oil Refineries, and the UK Digital Twin Project for Built Infrastructure.

All outstanding work in my opinion.

As a result, I was convinced of SpaceTime, not Space and Time. The advances in Science support this.

• https://www.blog.ajabbi.com/2023/08/matthew-west-1953-2023.html

As previously discussed on this forum, I reverse-engineered the material above and built my own Boro Engine (bor) for Pipi 9. It's not in production yet, but it works and can go forward and backwards. It uses 4D'ism SpaceTime in the underlying data model.

• https://www.blog.ajabbi.com/2024/12/dafni-conference-2024.html

There are a number of different spatial situations that require different kinds of optimised servers.

• The Universe (satellite navigation)
• Earth as a geography (GIS server)
• Inside buildings (CAD maybe??)
• etc

• https://www.blog.ajabbi.com/2025/11/workspaces-for-built-environment.html

The question now is how to make that work with a GIS Server for the world driven by a GeoDatabase using GeoServer and PostGIS+PostgreSQL.

• https://www.blog.ajabbi.com/2026/02/gis-mapping-options.html

Years ago, when NZERN received the ESRI Conservation Grant with all that GIS Software, I created geodatabases with a time column in every table to track changes.

• A forest might grow in extent over time
• A lake's composition might change over time without changing its extent.

I also hacked ESRI JTX as a way to store changes over time. (not what it was designed for)

Future work on Pipi 10 (2027)

I don't think GeoServer 3 has that spacetime functionality built in. But spacetime could be incorporated into GIS via the Geodatabase. I thought an SQL link between the Boro Engine (bor) database and the GIS Geodatabase might work.

I need to do some experiments

Will keep you posted

Mike Peters
NZ
https://www.blog.ajabbi.com

======================

Hi Mike,

Good to hear from you.

Be really useful to hear any experiences you have with geospatial systems in Pipi 9 and 10.

Chris

=================

Chris,
This is a great project. I need to use 4D Spacetime in Pipi 10 (the next version). I will read all this with great interest.

I have used a great deal of your and Matthew West's previous work. All excellent. Thank you.

Mike Peters
NZ
https://www.blog.ajabbi.com

[alex.shkotin]

Chris,

You've touched on several interesting topics for me. I'm not sure how interesting they are for you, though.

The first topic is defining the meaning of the term.

The term "Null Island" is interesting because, as far as I understand, it's not a standard, so to speak, theoretical term. At least, it's not in the glossary at https://www.iers.org/IERS/EN/Service/Glossary/glossaryStandard. However, there are many things missing there, and this is an interesting follow-up on the system of terms and their definitions in the IERS.

I understand that you use the term as a name for a point in the coordinate system with coordinates are 0°N 0°E. But if we look further in Wikipedia, under the heading "Physical location": "The point on the Earth's surface defined as Null Island is located in international waters in the Atlantic Ocean, roughly 600 kilometres (320 nmi) south of the West African coast in the Gulf of Guinea.[2]"

This means it's a name for a part of the Earth's surface with coordinates 0°N 0°E. This corresponds to the word "location" in the Wikipedia description you provided.

This leaves two different definitions for Null Island, not considering the third—the absence of coordinate values ​​for some object in the database.

It seems to me you're sticking to the definition:

Null Island is a proper name for a point in any coordinate system with coordinates 0°N 0°E, if such coordinates exist.

The system of terms and their definitions in the IERS is the core of the corresponding formal ontology.

Is this an interesting topic?

Alex

четверг, 5 февраля 2026 г. в 20:51:25 UTC+3, Chris Partridge:

[Joshua Lieberman]

Well, since Null Island is defined as a coordinate position and not a physical feature (“Null”!), it isn’t actually a geographic feature in the sense that a hilltop might be a discerned and discussed part of the universe that can be referenced in multiple ways (name, coordinates, directions, address, etc.). There is nothing to reference. I suppose it might be best to call it a “humorous feature”.

An abstract model of geographic features (General Feature Model) is embodied in both the OGC Abstract Specification and the corresponding ISO TC211 191nn specifications. It can always be improved, but probably does not need to be reinvented.

—Josh

On Feb 12, 2026, at 12:23 PM, alex.shkotin <alex.s...@gmail.com> wrote:



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[hpo...@verizon.net]

It’s not a feature at all. It has no physical existence. It is part of the conceptual reality created by human society (or some subset thereof – mostly British). It is just like the Prime Meridian and the Equator, namely the intersection of the two. The same goes for the entire coordinate reference system. The challenge is anchoring that conceptual reality to some piece of physical reality – like that island in the North Sea where some guys a long time ago decided they needed a longitudinal reference point for their maritime ambitions. Should have been the western tip of Iceland, not Greenwich, in my opinion. That way the international date line and the Prime Meridian could have been one and the same, and the connection to some physical prominence in physical reality would have been a bit less arbitrary and easier to spot from space.

 

Another problem is that the Earth isn’t really all that solid. It also wobbles and bulges, making the location of both the Prime Meridian and the Equator a bit problematic with respect to coupling them and the more general coordinate reference system to physical reality.

 

Hans Polzer

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[Alex Shkotin]

Joshua,

For me, there are three definitions of the term "Null Island": a name for a coordinate point in some coordinate system, a name for a location on Earth, and a name for invalid or missing geodata.

Since this term is used throughout Chris's post, it's important to understand which one he used.

I'm fairly certain this term isn't in the OGC Abstract Specification glossaries or the corresponding ISO TC211 191nn specifications.

It's a bit funny to me to start with such a term. But that's up to Chris.

You think Chris is sticking to the first definition. I think so too. But it's better to start with a clearly written definition of this term, since the next definition we need is that for the coordinate system Chris writes about and is a much more powerful thing.

Alex

пт, 13 февр. 2026 г. в 01:45, Joshua Lieberman <jo...@oklieb.net>:

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[Chris Partridge]

Hi Alex,

Yes, a very good catch. This is one of the core issues - and it might be good if you explained your reasoning in more detail as it will exemplify what is going on.

WRT: "Null Island is a proper name for a point in any coordinate system with coordinates 0°N 0°E, if such coordinates exist."

It is not for me to decide, but I wonder whether it would have to be a geographical earth bound coordinate system. 

The same kind of name that takes a coordinate system as a parameter would be needed for names such as 'equator', 'prime meridian' and so on.

And "0°N 0°E" is a label, a name, in the coordinate system namespace.

This is linked, ontologically, to what I see is at stake is the physicalization of the coordinate system geometry. 

This is well recognised in the history of relativity.

Simplifying a little: up until the late 19th century geometry was physical. Euclidean geometry was the (physical) geometry of space.

Starting in the late 19th century geometry became more formalised and abstract. Hilbert's axioms you mentioned earlier being one example.

This raised questions in physics of the role of geometry - and one of the achievements of relativity is to develop a way to physicalize coordinate systems - I'll add some quotes at the end to give more detail.

If you like the silo metaphor, then you can think of physics (relativity) and geodesy as developing in separate silos.

Most of the major foundations of geodesy were established in the 19th century and earlier. So, in its silo, there was no pressure to follow the path taken by physics (relativity). It assumes geometry is abstract and then devises some mapping to it.

When you start with separated space and time - then the geodesy position has a sort of internal consistency.

However, if you start with space time, the physics (relativity) position seems more intuitive. 

In space-time, once you start locating Null Island in space, it becomes an obvious step to locate it as a worldline in space time (the physics (relativity) view).

It is then an obvious next step to seeing each coordinate point as a worldline and the set associated with a coordinate system as a congruence.

If one wishes to reject the idealist interpretation, it is necessary to specify some objective physical subject matter for the theory. The most natural suggestion would be to take the subject matter of the theory as comprising those types of physical fact or process which figure in the construction of a coordinate system of the standard type. The theory would then be taken as an objective physical theory of those types of physical fact or process, independently of any epistemic use to which they might be put. 🔗

Mundy, B. (1986). The Physical Content of Minkowski Geometry. The British Journal for the Philosophy of Science, 37(1), 25–54.

… in Einstein's 1905 paper … The actual arguments are entirely concerned with the properties of coordinate systems, and Einstein makes quite explicit statements concerning how the coordinate systems are to be constructed, using rods, clocks, and light rays. If we follow the above suggestion of seeking for the physical subject matter of the theory among the types of physical fact which are involved in the construction of a coordinate system of the type referred to in the ordinary informal presentations, we are led to consider facts concerning rigid bodies, clocks, and light rays. 🔗

Mundy, B. (1986). The Physical Content of Minkowski Geometry. The British Journal for the Philosophy of Science, 37(1), 25–54. 

The use of material reference systems in general relativity has a long and noble history. Beginning with the systems of rods and clocks conceived by Einstein [1] and Hilbert [2], material systems have been used as a physical means of specifying events in spacetime and for addressing conceptual questions in classical gravity. That such systems also provide important tools for quantum gravity was pointed out by DeWitt [3], who used them to analyze the implications of the uncertainty principle for measurements of the gravitational field. 🔗

Brown, J. D., & Marolf, D. (1996). On Relativistic Material Reference Systems. Physical Review D, 53(4), 1835–1844.

 For this reason non-rigid reference-bodies are used which are as a whole not only moving in any way whatsoever, but which also suffer alterations in form ad lib. during their motion. Clocks, for which the law of motion is any kind, however irregular, serve for the definition of time. We have to imagine each of these clocks fixed at a point on the non-rigid reference-body. These clocks satisfy only the one condition, that the “readings” which are observed simultaneously on adjacent clocks (in space) differ from each other by an indefinitely small amount. This non-rigid reference-body, which might appropriately be termed a “reference-mollusk,” is in the main equivalent to a Gaussian four-dimensional co-ordinate system chosen arbitrarily. That which gives the “mollusk” a certain comprehensibleness as compared with the Gauss co-ordinate system is the (really unqualified) formal retention of the separate existence of the space co-ordinate. Every point on the mollusk is treated as a space-point, and every material point which is at rest relatively to it as at rest, so long as the mollusk is considered as reference-body. The general principle of relativity requires that all these mollusks can be used as reference-bodies with equal right and equal success in the formulation of the general laws of nature; the laws themselves must be quite independent of the choice of mollusk. 🔗

Einstein, A. (1920). Relativity: The Special and the General Theory: A Popular Exposition.

--

[Alex Shkotin]

Hans,

That's right. And one of the things Chris might be referring to is that the coordinate system associated with the Earth moves with it, always remaining at its center of mass and rotating its axes to best match the motion of the Earth's surface.

What location on the Earth's surface 0N oE falls at at a given moment in this coordinate system might be interesting.

But I haven't yet figured out what coordinate system Chris is talking about.

Alex

пт, 13 февр. 2026 г. в 02:12, hpolzer via ontolog-forum <ontolo...@googlegroups.com>:

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[Chris Partridge]

Hi Josh,

I wonder whether we need some kind of overhaul.

WRT: "Well, since Null Island is defined as a coordinate position and not a physical feature (“Null”!), "

The term 'Null' could be referring to the label '0' humourously - rather than the feature?

I'm guessing that feature is an overloaded term for you - see definitions below.

So some questions:

Is a coordinate position physical? (And is it the same as a coordinate point?)

You say "There is nothing to reference." are you suggesting that there is nothing physical there?

https://isotc211.geolexica.org/concepts/168/ --- feature
abstraction of real world phenomena
Note to entry: A feature may occur as a type or an instance. Feature type or feature instance shall be used when only one is meant.
[SOURCE: ISO 19101-1:2014]

https://isotc211.geolexica.org/concepts/419/ --- spatial object
object used for representing a spatial characteristic of a feature
[SOURCE: ISO 19107:2019]

https://isotc211.geolexica.org/concepts/703/ - coordinate reference system
coordinate system that is related to an object by a datum
Note to entry: For geodetic and vertical datums, the object will be the Earth.
[SOURCE: ISO 19111:2019]

https://isotc211.geolexica.org/concepts/2038/ - coordinate
one of a sequence of numbers designating the position of a point
Note to entry: In a spatial coordinate reference system, the coordinate numbers are qualified by units.

[SOURCE: ISO 19111:2019]

https://isotc211.geolexica.org/concepts/93/ - coordinate system
set of mathematical rules for specifying how coordinates are to be assigned to points
[SOURCE: ISO 19111:2019]

https://isotc211.geolexica.org/concepts/347/ - position
data type that describes a point or geometry potentially occupied by an object or person
Note to entry: A direct position is a semantic subtype of position. Direct positions as described can only define a point and therefore not all positions can be represented by a direct position. That is consistent with the "is type of" relation. An 19107 geometry is also a position, just not a direct position.
[SOURCE: ISO 19133:2005]

https://isotc211.geolexica.org/concepts/349/ - positioning system
system of instrumental and computational components for determining position
Note to entry: Examples include inertial, integrated, linear, optical, and satellite positioning systems.
[SOURCE: ISO 19116:2019]

https://isotc211.geolexica.org/concepts/1166/ - geographic point location
well defined geographic place described by one coordinate tuple
[SOURCE: ISO 19145:2013]

https://isotc211.geolexica.org/concepts/1167/ - geographic point location representation
syntactic description of a geographic point location in a well known format
[SOURCE: ISO 19145:2013]

https://isotc211.geolexica.org/concepts/1376/ - grid coordinate reference system
coordinate reference system for the positions in a grid that uses a defined coordinate system congruent with the coordinate system described by the GridEnvelope and axisLabels of gml:GridType
Note to entry: A grid CRS uses a defined coordinate system with the same grid point positions and origin as the GridEnvelope, with the same axisLabels, but need not define any limits on the grid size. This coordinate system is sometimes called the internal grid coordinate system.
[SOURCE: ISO 19136-2:2015]

https://isotc211.geolexica.org/concepts/419/ - spatial object
object used for representing a spatial characteristic of a feature
[SOURCE: ISO 19107:2019]

https://isotc211.geolexica.org/concepts/1178/ - spatial position
direct position that is referenced to a 2- or 3-dimensional coordinate reference system
Note to entry: An alternative to specifying a location as a linearly referenced location.
[SOURCE: ISO 19148:2021]

https://isotc211.geolexica.org/concepts/424/ - spatiotemporal object
object representing a set of direct positions in space and time
[SOURCE: ISO 19123:2005]

https://isotc211.geolexica.org/concepts/214/ - geometric object
spatial object representing a geometric set
Note to entry: A geometric object consists of a geometric primitive, a collection of geometric primitives, or a geometric complex treated as a single entity. A geometric object may be the spatial representation of an object such as a feature or a significant part of a feature.
[SOURCE: ISO 19107:2019]

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[Chris Partridge]

Hans, Alex, 

WRT: "Another problem is that the Earth isn’t really all that solid. It also wobbles and bulges, making the location of both the Prime Meridian and the Equator a bit problematic with respect to coupling them and the more general coordinate reference system to physical reality."

Yes, there are a whole host of metrological ('measurement' not 'being') challenges. However, these are (mostly) orthogonal to this topic.

WRT: "It’s not a feature at all. It has no physical existence. It is part of the conceptual reality created by human society (or some subset thereof – mostly British). It is just like the Prime Meridian and the Equator, namely the intersection of the two. The same goes for the entire coordinate reference system."

This is one ontological choice - and it is good to surface it.

It is not the only ontological choice, and I prefer what might be a different one - one where there is a physical spacetime manifold. So a substantivalist approach to time - see e.g. https://plato.stanford.edu/entries/spacetime-theories/ - actually I prefer a supersubstantivalist view - (like possibly Descartes - https://plato.stanford.edu/entries/descartes-physics/ ) - but this is not so relevant to the argument.

@Hans, is your ontological position that the 0°N 0°E for a specific coordinate system has no physical existence - or do you allow that it exists, but that its naming is at some level arbitrary, the results of human activity. 

Once you allow that it has a physical existence, would you agree that you can then ask about how the spaces at a time relate to spacetime? And that the natural next step is (as done in relativity) to regard it as a physical worldline?

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[Joshua Lieberman]

I emphasize again that “Null Island” is a bit of irony, since not only is there no “Island” but the physical position of [0,0] is going to be different for each coordinate reference system. So of course the phrase doesn’t occur in the glossary of foundational standards on defining and referencing geographic features. “Feature” itself is a multiply defined term. In machine learning it refers to model parameters. This causes immense confusion in the case of geospatial ML models.

The physical Earth is indeed very irregular, but the Earth’s surface is also always changing and moving with plate tectonics and even the gravitational influence of the moon. The actual shape  of that surface is termed the “geoid”. Geographic coordinate reference systems and the datums they are built on are formally defined as ellipsoids, which are then variously corrected to approximations of the geoid, using in some cases networks of  well-studied, continuously updated reference points (HARN). Geodetics are complicated, even (especially?) for geographers.

For anyone  who has visited  Greenwich, England, there is amusingly an actual physical representation of the Prime Meridian across the observatory, which in that sense makes it a real geographic feature, at least over the span of 50 feet or so.

—Josh

On Feb 13, 2026, at 6:22 AM, Chris Partridge <partri...@gmail.com> wrote:



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[Chris Partridge]

Hi Josh,

Agree there are all sorts of metrological hurdles to overcome.

WRT: the physical position of [0,0] is going to be different for each coordinate reference system.

The ontological *rather than geodetical) point I am pursuing is how one should characterise this physical position for a particular coordinate reference system.

Is it a point in space (one that has different manifestations at different times)?

Is it a worldline in spacetime (as relativity would suggest)?

Do you have any intuitions about this?

Best,

Chris

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[John F Sowa]

Ontology is the study of everything that exists, may exist, or cannot exist anywhere in the universe at any time or location.   Issues about any particular galaxy, solar system, or planet, or any location on any of them are extremely important for practical issues.   But they are application-dependent issues.  They are not fundamental ontological issues.

Re coordinate reference systems:  They are very important for practical applications.  But every spatial coordinates of any kind are always application dependent.  Any system for any planet or star or galaxy or any part of any of them, no matter how big or how small, is always a special case.  No universal system is possible.  Practical issues for relating different systems are essential for applications, but they are not fundamental in theory.

The above paragraphs summarize some of the issues on which Doug Lenat and I were in strong agreement ever since 1993, when I published a review of his book:  D.B. Lenat and R.V. Guha, Building Large Knowledge-Based Systems: Representation and Inference in the Cyc Project

Lenat began that project in 1984.  Then he and Guha published that book in 1990.  In 1993, five AI experts published reviews in the Journal Artificial Intelligence.  Lenat later sent me a note saying that my review was the most accurate, but also the most painful -- because I discussed every unsolved problem that they were still hoping to solve in some way.

For years afterward, Lenat and I were working on different projects with different foundations and methodologies, but we basically agreed on the fundamental issues.  We both agreed on the basic issues in that review, which are still relevant today.

The closing paragraph in that review is just as relevant today as it was in 1993: Finally, the question of whether Cyc could ever achieve true common sense at a human level is an interesting theoretical issue, but it's irrelevant for many applications. Database systems, for example, are not at all human-like in their ability to store and dispense large volumes of knowledge. In fact, their very nonhuman characteristics are what make them so valuable. But their lack of human friendliness makes them hard to learn and use. Some amount of background knowledge might help to make them friendlier and more flexible, even if it was far from a truly human level of common sense. If Cyc could become a general help facility that could organize knowledge about any application running on a computer, that would be sufficient to realize Lenat's hopes that no user would want to be without it. 

John

[John F Sowa]

I forgot to include the reference to the book review I cited in the paragraphs below:  https://www.jfsowa.com/pubs/CycRev93.pdf .

 

Ontology is the study of everything that exists, may exist, or cannot exist anywhere in the universe at any time or location.   Issues about any particular galaxy, solar system, or planet, or any location on any of them are extremely important for practical issues.   But they are application-dependent issues.  

[hpo...@verizon.net]

Chris,

 

My perspective on coordinate reference systems is that they have no physical existence and are not detectable by physical sensory means unless we humans create phsycal means to do so. An alien UFO approaching Earth from points unknown will have no means to detect a coordinate reference system we create unless they establish some means of communicating with humans or interpreting human artifacts that embody the coordinate reference system in some way, such as the Prime Meridian monument. The UFO pilot will certainly not be able to detect the “null island” feature.

 

Coordinate reference systems can be anchored to some physical entity by convention/agreement among those who want to use such a coordinate reference system to facilitate communicating relative locations of physical or conceptual entities (e.g, school zones, congressional districts, etc). That’s what the British did when they created the Prime Meridian and associated monument. Of course, continental drift, tidal forces, and other internal semifluidic movements inside the earth make that monument a bit of a moving target with respect to other  objects on the surface of the earth or in space around the earth.

 

Alex points out that one could instead use some center of mass of the earth as the center of the coordinate reference system, presumably calculated by using some dynamic physical model of the earth informed periodically or continuously by some battery of sensors, likely space based. That’s probably sufficient for using the coordinate reference system for orbital dynamics, possibly using the sun-earth line as a longitude reference point. But that still leaves the issue of earth’s motion around it’s spin axis and the coupling of the coordinate reference system to surface features if it is to be used to locate objects with respect to each other on Earth’s surface. And many people will still want to locate orbital/near-space objects with respect to points on the Earth’s surface. Some physical surface monument(s) are still required, albeit they might need to be “adjusted” over time like we do with our calendar and clocks to incorporate the vagaries of Earth’s orbit around the sun and it’s varying and slowing spin.

 

This also points out that there is a lot of coupling between coordinate reference systems and our clocks and time zones, which is why viewing such systems as a 4D construct is good. That’s also why I suggested that the International Dateline and the Prime Meridian should really be one and the same conceptual construct. Of course, pragmatics dictate that such a construct should not bisect an area of significant population density, if at all possible.

Greenwich England doesn't meet that criteria.

 

I don’t really have a position on coordinate reference systems relationship to spacetime other than to point out the anchoring problem for them to be useful. We naturally use the Earth and the sun as an anchors, but astronomers and astrophysicists have developed other anchors to support galactic and universe level relative location and movement analysis of the entities we see in space.

 

Hans

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[hpo...@verizon.net]

 

Prime Meridian Monument in Greenwich, England

 

Josh,

 

Thanks for elaborating a bit on the geoid and geodetics. I didn’t want to take the time myself to go into all that and left it as “the Earth isn’t really all that solid”. And as you point out, some of the bulging is due to tidal forces, and not just from the moon. I thought you might like the picture above.

 

Hans

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[John F Sowa]

Hans,

I agree with your comments below . 

General principle;  The choice of coordinate system is not an issue of ontology, but of the  kinds of applications that use the ontology.   A very general ontology might be applied to anything from subatomic particles to enormous galaxies billions of light years away.  One size does not fit all -- nor does any particular reference point.

Following is a paragraph that I sent in a previous note to the thread:

Re coordinate reference systems:  They are very important for practical applications.  But every spatial coordinates of any kind are always application dependent.  Any system for any planet or star or galaxy or any part of any of them, no matter how big or how small, is always a special case.  No universal system is possible.  Practical issues for relating different systems are essential for applications, but they are not fundamental in theory.

John

____________________________

[hpo...@verizon.net]

John,

 

I concur. I saw your earlier email after I wrote the response below and was tempted to respond, but I think what I wrote pretty much said the same thing, albeit not in so many words. Of course, I was coming at it from a pragmatic application perspective and not from an ontological viewpoint.

 

Hans

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[Alex Shkotin]

Chris,

Many interesting topics have been raised, but I'll mention just three:

- "worldline." When you talk about a worldline, you're most likely talking about a geometric representation of the law of motion, for example, of a particle. So, if the motion is one-dimensional, like a cannonball falling, then in a two-dimensional R×T space, its worldline will be a parabola.

- GPS is a complex modern engineering system, and one of the interesting questions is obtaining the geographic coordinates of a receiver based on its measurements. I discussed this with chatGPT – you might find it interesting https://chatgpt.com/s/t_69904996ca488191af08a14c2e203df8 

- Referring to the "mollusk" in Einstein's popular work isn't the best approach – it's better to refer to the theory itself, where everything is much more sophisticated. However, I wouldn't delve into general relativity yet – it's a very strong mathematical abstraction of determinism https://chatgpt.com/s/t_69904a5ccc508191936bc4b7d142e176 Sorry, it's in Russian, but I can not translate it right now.

By the way, the links like https://borocvi.atlassian.net/wiki/spaces/4G/pages/6499205137/reference-mollusk  you gave are blocked for Russia.

Alex

пт, 13 февр. 2026 г. в 13:35, Chris Partridge <partri...@gmail.com>:

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[Chris Partridge]

Hi John,

Thanks for the comment.

WRT:  But every spatial coordinates of any kind are always application dependent.  Any system for any planet or star or galaxy or any part of any of them, no matter how big or how small, is always a special case.  No universal system is possible. 

In one sense, the geodesic sense, you are quite right. Coordinate systems are built from a datum - and the metrology for doing this is impressive and sophisticated. And it is related to our human interests. Similarly, one could argue that the specifics of evolution of earth are more history than science (as Popper pointed out). There is the limit case, the coordinate system for the universe, this, by definition, is universal.

There is another sense that this comment misses. In relativity (physics) 4D coordinate systems are a key component of the science (and they make clear that the coordinate labels are arbitrary - a gauge property). In fact, you could say that one aspect of general relativity is that every (rigid) object has a relative space that is a basis for its own coordinate systems. Similarly, these evolve into 3D systems - see e.g. https://en.wikipedia.org/wiki/ADM_formalism. In this sense, coordinate systems seem to be part of general physics.

Of course, there is no guarantee that aliens will always make the same scientific journey as us, but surely it is possible some will have at some stage a physics similar to our relativity.

The point you make relates to my interest.

I think there are universal approaches to coordinate systems, well exemplified in physics/relativity. And that we should try, as far as we can, to use these 'patterns' when dealing with the more parochial concerns of earth-based systems. I would be odd to exclude whole branches of physics from ontology.

WRT: Ontology is the study of everything that exists, may exist, or cannot exist anywhere in the universe at any time or location.  

Yes, exactly. I like Jonathon Lowe's version of this: 

"the set of things whose existence is acknowledged by a particular theory or system of thought."
Lowe, E. J. (1995). Ontology. In T. Honderich (Ed.), The Oxford companion to philosophy. Oxford University Press.

And so I am asking if we have a 'theory' (where a geospatial computer system such as PROJ would count as a theory), which includes commitments to a coordinate system, including individual coordinates, what is this theory committing to?

As I said earlier, "Plato and Aristotle have a process that starts with the  "τί ἐστι" (ti esti, "what is it?") question - and it seems a good way in here." So my methodology) is to ask this for the simplest case I can find, so I can surface the assumptions being made.

What is also relevant here is that geodetic coordinate systems are much better practical examples of the coordinate pattern than physics - though I believe the underlying patterns are much the same. 

Best,

Chris

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[Chris Partridge]

Hi Hans,

Thanks.

WRT: I don’t really have a position on coordinate reference systems relationship to spacetime other than to point out the anchoring problem for them to be useful. We naturally use the Earth and the sun as an anchors, but astronomers and astrophysicists have developed other anchors to support galactic and universe level relative location and movement analysis of the entities we see in space.

Agreed. Anchoring (or realising) the geodetic datum is an essential step in the metrology of coordinate systems.

WRT: My perspective on coordinate reference systems is that they have no physical existence and are not detectable by physical sensory means unless we humans create phsycal means to do so. 

Prima facie this sounds right. But I think if we dissect it carefully, things are less clear.

If our ontology has a spacetime-matter divide, then it is probably practically true that matter is easier to identify and measure than spacetime. Though we do have instruments that measure attributes of spacetime e.g. its curvature. 

There are theories in physics that physicalise spacetime quite clearly, an example is causal set theory (https://en.wikipedia.org/wiki/Causal_sets).

So, very general theories (such as relativity) postulate coordinate systems that exist independently of us. Are you constructivist about these? Or is it the labelling of the coordinate points that is constructed?

Chris

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[hpo...@verizon.net]

Chris,

 

I don’t think that spacetime itself is a useful coordinate reference system, the key word being “reference”, by its very nature – and the nature of relativity. An entity can “sense” local spacetime curvature by accelerometers, but that tells it nothing about what some other entity is experiencing unless they are collocated or it knows something about the objects that might be causing the local curvature of spacetime. If spacetime is locally “flat” the only useful reference point is the entity itself. Every entity in spacetime is its own coordinate reference system. Other entities can only use that coordinate reference system if they know where they are located in it or vice-versa. That means we naturally gravitate (had to use that) to highly curved space time loci as the bases for coordinate reference systems intended for sharing location information between/among entities.

 

Of course, we also have lots of systems that use individual entity-based coordinate reference systems such as radars to locate objects with respect to themselves. But for these systems to be useful to others, we need to map/translate these locations to coordinate reference systems that other systems/entities can use. And that typically means we have to use a frame of reference that is shared with and understood by those other entities.

 

I think it may be useful to consider how general relativity and spacetime concepts  impact and inform coordinate reference systems in developing an ontology for them, at least at macroscopic scales. I just have trouble envisioning how spacetime itself could be “the” coordinate reference system. Then again, I don’t pretend to have a deep understanding of general relativity concepts.

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[John F Sowa]

There is no such thing as a universal coordinate system.  You don't use the same coordinate system with a microscope, a telescope, a train, a plane, or your car on the highway.

Suppose you're driving a Tesla or other car with all the latest gimmicks.  The most important coordinate system is centered on your car and its position relative to the road, other vehicles, and various things (static or mobile) near your car.  The next most important coordinate system is based on information about the immediate neighborhood and about the roads from your starting point to your destination.

All this debate about some theoretical point on the equator is totally irrelevant for 99.99% of practical applications on earth and 100% irrelevant for anything outside the earth or inside any building on earth.

Summary:  The number and kinds of coordinate systems is unlimited, and none of them can be considered fundamental for ontology.  But the problem of relating different coordinate systems is a very important practical issue.

John

 

---

From: "Chris Partridge" <partri...@gmail.com>

[Chris Partridge]

Hi Hans,

WRT:  I don’t think that spacetime itself is a useful coordinate reference system, the key word being “reference”, by its very nature – and the nature of relativity

I think I understand what you mean here, and spacetime itself is maybe not enough to be useful. But there are a number of coordinate systems that are used for positioning in spacetime, including:
ICRS — International Celestial Reference System
BCRS — Barycentric Celestial Reference System
ECI — Earth-Centered Inertial Frame
GCRS — Geocentric Celestial Reference System
GPS (USA) -Solves for (x, y, z, t) using signals from ≥4 satellites.
Galileo (EU) - Same 4D positioning principle as GPS.
GLONASS (Russia) - 4D satellite trilateration system.
BeiDou (China) - Full 4D global navigation system.

The ICRS is intended to approximate a global inertial frame - so a single preferred frame.

In relativity/physics it seems to be standard practice to talk about coordinates for spacetime - some random quotes below (the copying may not have always preserved the formatting). However, they are clear that these are labels and so in some sense chosen (gauge) not 'physical' (maybe in a sense similar to your constructivism).

Ch. 1. INTRODUCTION
§ 1.1. The Problem Defined
2. Coordinate systems, frames of reference and relative spaces. When Einstein wrote of a four-dimensional space-time coordinate system or reference system—terms which he used interchangeably—it is by no means clear whether he should be read as referring to what we now call a coordinate chart of the space-time manifold, a frame of reference (a congruence of timelike curves), or a relative space (a three-space defined by a frame of reference); see Norton.(40)
Norton, J. (1989). Coordinates and covariance: Einstein’s view of space-time and the modern view. Foundations of Physics, 19(10), 1215–1263. https://doi.org/10.1007/BF00731880

Ch. 3. On Reference Systems and Relative Spaces
In this section, I will deal with structures associated with the semi-Riemannian manifolds of special and general relativity.
In such manifolds, it is now customary to represent the intuitive notion of a physical frame of reference as a congruence of timelike curves. Each curve represents the world line of a reference point of the frame. The velocity of these points is given by the tangent vectors to the curves, where defined. We shall usually deal with frames of reference in rigid-body motion and we can readily nominate the state of motion of such frames because of the limited number of degrees of freedom associated with them.7 In particular, an inertial frame of reference in a Minkowski space-time is a congruence of time-like geodesics in rigid-body motion. and therefore its reference points move with constant velocity.
A coordinate system {xi}(i = 1, 2, 3, 4) is said to be “adapted” to a given frame of reference just in case the curves of constant x1, x2, and x3 are the curves of the frame. These three coordinates are “spatial” coordinates and the x4 coordinate a “time” coordinate.
(Norton 1985 What was Einstein’s principle of equivalence?) Studies in History and Philosophy of Science Part A, 16(3), 203–246.

Ch. 2 The Invariance Principle
Partly, this is because the idea of a reference frame is really quite different from that of a coordinate system. Frames differ just when they define different spaces (sets of rest points) or times (set of simultaneous events). So the ideas of a space, a time, of rest and simultaneity go inextricably together with that of a frame. However, a mere shift of origin, or a purely spatial rotation of space coordinates results in a new coordinate system. So frames correspond, at best, to classes of coordinate systems. However, beyond all this, the ontology connected with the idea of frames is different from spacetime ontology.
Nerlich, G. (1994). What spacetime explains: Metaphysical essays on space and time. Cambridge University Press

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[hpo...@verizon.net]

Chris,

 

I believe the list of coordinate systems you provided meets the description I provided in my previous email: “That means we naturally gravitate (had to use that) to highly curved space time loci as the bases for coordinate reference systems intended for sharing location information between/among entities”. In some cases, they are using sets of such loci, but the basic idea is similar.

 

It will be interesting to see where your efforts in this area will lead.

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[Chris Partridge]

Hi Hans,

Many thanks.

Chris

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[Chris Partridge]

Hi John,

I think the point of this tread may not be clear. Let me try to make it clearer.

Firstly, I am not making any claims the coordinate systems are fundamental to ontology. However, I do think they are fundamental to the ontology of various domains, including the geospatial domain, and so useful. Hence Barry's earlier comment.

However, at the heart of the issue is something fundamental, the treatment of space and time and so spacetime.

As I have noted in many other places, there is a metaphysical choice when building your foundations, whether to separate or unify space and time (see e.g https://www.cdbb.cam.ac.uk/files/a_survey_of_top-level_ontologies_lowres.pdf - 4.2.2.1 Spacetime). As we know, and undergraduate textbooks point out, these metaphysical choices then permeate the way we think of the world.

Modern physics (since the early 20th century) has, in the study of relativity, clearly taken the unifying route and worked with spacetime - and built into that theories that recover the notions of spaces and times. Part of the apparatus for this research has been coordinate labels (as the earlier quotes show) - and the philosophy of physics discusses the ontology of these labels.

Modern geodesy, in contrast, seems to have stuck with a separating of space and time strategy/choice.

I am using the simple example of Null Island to, among other things, get people to think and talk about how their own ontology has finessed the unifying or separating space, time and spacetime metaphysical choice. This is surely in the spirit of other thought experiments, such as Galileo's ship (https://en.wikipedia.org/wiki/Galileo%27s_ship).

On a more practical level, I am hoping to show that there are opportunities to develop geospatial ontology - aligning it more with relativity ontology.

Surely, this is an interesting and useful endeavour.

Chris

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[Ravi Sharma]

Chris

• We are considering relativistic effects that require Spacetime and special relativity.
• Astrophysical observations and areas such as galactic and intergalactic spaces affected by large mass variations and warps may require General Relativity which is multidimensional and tensorial.
• What will be the use cases, such as "Null Island" and Geodesy-type observations in inertial frames?

Energetic cosmic rays and particles are close to the physics use cases I can think.

Regards.

Thanks.

Ravi

(Dr. Ravi Sharma, Ph.D. USA)

NASA Apollo Achievement Award

Former Scientific Secretary ISRO HQ

Ontolog Board of Trustees

Particle and Space Physics

Senior Enterprise Architect

SAE Fuel Cell Standards Member

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[Chris Partridge]

Hi Ravi,

Great question.

I suspect you know much more about this than me.

In the Null Island case, well in each Null Island realisation, you are making a spatial projection (based on the geodetic datum). This spatial projection is built up from individual coordinates.

You get the same structures in relativity.

Every time you work in a 4D coordinate system, you have an implicit spatial projection (by dropping the time coordinate). The coordinate system needs a spatial foliation.

And if you have a time coordinate, this also implies a time foliation.

Any use of a local coordinate system, implies a relative space - and so a spatial projection see 3+1 (ADM) formalism (https://en.wikipedia.org/wiki/ADM_formalism).

For example, in measurement theory, I would expect that any operational measurement in relativity ultimately involves spatial projection: distances are measured in the observer's rest space, relative velocities are spatial projections of 4-velocities, and radar distances involve round-trip light signals analyzed in the observer's local spatial geometry.

I think that you, with your physics background, should already be thinking of spatial coordinates as worldlines. It should be a natural way of thinking. It would be great if you could confirm this.

Then the interesting question is how do people with your perspective engage with the geodesy community where they do not. Coll has some papers that might help. 
Coll, B. (2006). Relativistic Positioning Systems. AIP Conference Proceedings, 841, 277–284. https://doi.org/10.1063/1.2218182
Coll, B., Ferrando, J. J., Morales, J. A., Kunze, K. E., Mars, M., & Vázquez-Mozo, M. A. (2009). Emission coordinates in Minkowski space-time. AIP Conference Proceedings, 225–228. https://doi.org/10.1063/1.3141268

Best,

Chris

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[hpo...@verizon.net]

You are welcome, Chris.

 

By the way, you might want to consider analyzing how the coordinate reference systems you cited differ from each other. What are the attributes/features of each that are not found in the others or where they use different conceptual models. How do they differ in their scope of applicability? In what range of attributes do their implicit assumptions  become problematic? What are the signs that one is using the incorrect coordinate reference system for one’s application? How do application attributes relate to the scope of applicability attributes of a given coordinate reference system?

 

I think of these kinds of questions as being similar to defining/specifying  the performance envelope of an airplane or spacecraft. Where, when, and how can I use these different coordinate reference systems? When/where will they cause me to crash or lead me astray in what I am trying to use them for.

 

How/where do they overlap and how does one map from one to another, and where/when is that possible?

 

Some of these questions will have binary yes/no answers, while others will have quantitative answers and yet others will have subjective or application-specific  answers.

 

These answers  may help your ontology for coordinate reference systems to be more comprehensive and useful to those who have to deal with deciding what coordinate reference systems to use (or possibly develop) and how to work with multiple different coordinate reference systems if their application requires them.

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[John F Sowa]

Hans and Chris,

There is no limit to the number of different coordinate systems that may be required for just a single application. 

 As an example, I recently rode in a taxi that happened to be a Tesla.  While the driver was guiding the car through normal traffic, I was watching the screen on his right (easy to see from the back seat).  i realized that the computer that ran the display was using multiple coordinate systems simultaneously.  

On the left of the screen, the display showed the car itself at a fixed position near the bottom of the screen.  That seemed to be position (0,0) in a coordinate system centered on the car.  Nearby vehicles on the same road were shown in positions relative to our car.

To the right of that display, the driver could view other options.  For most of the ride, he could see maps of side roads that he might choose.  The scale of those maps included much more territory.  The names or numbers of the roads were shown and buildings or other features were also shown. 

All this information came from satellites orbiting high above, and other coordinate systems must have been relating the positions of our car on the ground to some satellite above.   That satellite must have been communicating with many other vehicles simultaneously.  It must have been creating and relating coordinate systems for many vehicles simultaneously.

As another example, our local ShopRite, where we get our weekly supply of food and other household items, now has robots that roll along through the aisles to take inventory of everything on the shelves.  There is a lot more to consider about relating the coordinate systems of multiple moving robots to the static coordinate system of the entire store.  None of those coordinates would need to be related to anything outside the store.

Summary:  The number of different coordinate systems that may be useful is far greater than the number of people and things for which a coordinate system might be useful.

John

____________

 

From: "hpolzer via ontolog-forum" <ontolo...@googlegroups.com>

[hpo...@verizon.net]

John,

 

I agree with your observations. Nonetheless, explicit thinking about the possible variability of coordinate reference systems can make any ontology of coordinate reference systems more useful. It’s OK to have a narrower focus for a particular product or project application. Nothing of consequence is produced without considerable focus. But it can be made more extensible and interoperable if you start with an awareness of the larger world in which it may be asked to work. That’s all that I am suggesting with my “thought experiment” questions. Just realize how narrow your focus actually is before committing a lot of effort into it - instead of being surprised at what you hadn’t considered after you built it.

 

Hans

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[John F Sowa]

Hans,

I think we agree about what to do and how to do it.

My only point is that the choice of coordinate system depends primarily on the application.  The same basic ontology may be used with an open-ended variety of coordinate systems for different kinds of applications.

For example, the clothing that a group of astronauts are wearing on earth is the same as what they're wearing on a trip to the space station, and it's the same as what they're wearing when they arrive.  The choice of coordinate system is irrelevant to its ontology.

John

_________________

[hpo...@verizon.net]

John,

 

I am simply responding to what Chris wrote about 10 days ago that started this thread:

 

“We are now revisiting some work on the ontology of coordinate reference systems - and the notion of a ‘spatial object’ - that we started around 15 or so years ago. Now, as we look a little more closely at the details quite a few questions emerge. I’m wondering whether there are people in the community with views on the topic, would be good to hear any thoughts.”

 

My interest was piqued enough by the “null island” discussion as I have had quite a few real world experiences with multiple different map graphics software packages for digital plotters (before they became commodities) and 0,0 lat/long issues, different map projections, crossing the equator, mapping accuracy at the poles, etc., so I jumped in when Josh Lieberman made his comments about the null island being a “humorous feature”.

 

I only have what Chris wrote and cited to infer what he envisions an ontology of coordinate reference systems to be, and I am offering up my thoughts to help him better explore what such an ontology might address.

 

Hans

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[Chris Partridge]

Hi Hans,

WRT: By the way, you might want to consider analyzing how the coordinate reference systems you cited differ from each other. 

Exactly. We are looking at this. It seems to us that the current databases often choose a simple pattern and shoehorn in the various coordinate systems. We are trying to better understand the underlying foundations that give rise to the patterns of variation. However, it all depends upon the details of how you build up the coordinate system. Hence, the null island question - which highlighted how two systems can differ. 

A good example of this is axes. In the case of Cartesian systems, one can physicalise the axes as lines. In the case of other types, there is not always an obvious physical line. We are looking at whether we can treat foliations of coordinate surfaces as the 'axes' - and this works nicely. It also fits in neatly with geometric patterns of foliation. To generate the coordinate system label, one needs to order the axes, for example, <lat, long> is not the same as <long, lat>. For simplicity, some databases make the order an essential attribute of the axis (see e.g. https://epsg.io/106-axis). However, from an ontological physical point of view the axes are prior to the order - and the same axes can participate in multiple ordering. 

Vis a vis the airplane/spacecraft systems. We have looked at these in the past focusing on ships and their datums - as reported in our papers. These types appear in the database of coordinate systems. However, for the initial stage of our work we are focusing on the core cases of broadly accepted geodetic systems, to make sure we get the underlying patterns straight.

Thanks again for your comments.

Chris

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[Chris Partridge]

Hi John,

WRT: My only point is that the choice of coordinate system depends primarily on the application.  The same basic ontology may be used with an open-ended variety of coordinate systems for different kinds of applications.

Agreed. There is (or should be) a framework or pattern for coordinate systems, that you are able to deploy in whatever application is needed. (As an aside, I think relativity's relative spaces play a part in that framework, in that every coordinate system is based upon a relative space).

The question is, what is that framework or pattern? And, I'm suggesting that we start investigating that by looking at very specific cases. If these turn out to be obvious or trivial, we can move on. If we find they raise questions, we should look into how they are answered.

Chris

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[hpo...@verizon.net]

Chris,

 

Just to be clear, I brought up the concept of “performance envelopes” for aircraft and spacecraft to illustrate the notion of a multi-dimensional “utility” or “applicability” space for a given construct, not as potential users of coordinate systems (which, of course, airplanes and spacecraft also are). Aircraft, for example, have lots of different performance dimensions, such as altitude range, stall speed, endurance, top speed, load capacity, fuel economy, cruising speed, distance range (related to cruising speed and endurance), takeoff weight, landing weight, takeoff and landing distances, air turbulence wake size, runway loading , climb rate, air temperature (which affects many of the other dimension points), etc. just to name a few key dimensions. What are the similar performance or applicability context dimensions for coordinate reference systems?

 

In other words, what is the applicability space of a given coordinate reference system? What are its significant applicability dimensions and what are the appropriate scales for each such dimension, and what are the values along those dimensions where the coordinate system is suitable or performs well? Where are the edges of that multi-dimensional space where the use of the coordinate reference system is questionable or definitely not advised. You can think of it as creating a coordinate reference system for coordinate reference systems, if you like.

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[Chris Partridge]

Hi Hans,

Interesting. I think I can see some of what you are after.

Let me see if I understand. 

People typically just default to aWGS84 based system. But this is linked to the crust in the western hemisphere. So, for example, in New Zealand it is not accurate for some tasks - such as cadastral records. See https://www.linz.govt.nz/guidance/geodetic-system/coordinate-systems-used-new-zealand/geodetic-datums/world-geodetic-system-1984-wgs84 --- "The tectonic plates under New Zealand move about 5cm per year, so the WGS84 coordinates are constantly changing. This means that coordinates in terms of WGS84 need to have a time associated with them (t), particularly when high accuracy is required." More generally, one can work out the differences between the coordinate systems and how these will vary over time using standard geospatial tools. In relativity, this is https://en.wikipedia.org/wiki/Rapidity --- Mathematically, rapidity can be defined as the hyperbolic angle that differentiates two frames of reference in relative motion, each frame being associated with distance and time coordinates.

Would this count as a kind of envelope?

There is another interesting aspect in the use of coordinate systems. It is common in geospatial systems to have a spatial geometric counterpart of some feature (a point, line or polygon in some coordinate system). When picking the counterpart, one needs to have some idea how this might be used as the accuracy can vary. So a ship radar position coordinate might be accurate for a second, but not for an hour. Similarly, a 2d aircraft coordinate might be okay for measuring distance travelled on the surface, but misleading if you want 3d distances. Often you want mereotopopological comparisons, again the accuracy required of this will dictate how you set up the spatial geometric counterpart.

So, using your terminology (maybe correctly) there are some inherent 'performance' characteristics that one should be aware of when working with coordinate systems.

And, yes I agree these types of things are important issues to get clear (assuming I have understood your point).

Chris

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[hpo...@verizon.net]

Yes, exactly. And you can see that the number of possible dimensions  of the performance/applicability space and associated value sets can be quite large. In the mapping domain, drawing a straight line on a Mercator map does not give you the correct course azimuth from point A to point B. In Lambert Conformal Conic map projection maps it does, which is one reason that projection is used for aeronautical charts. An interesting exercise would be to list how the different coordinate reference systems differ from each other inherently (e.g., radial vs rectilinear) and with respect to common applications of them (e.g., near-earth space tracking, earth surface navigation, inter-stellar research, etc.).

 

And the different dimensions/attributes may only be “semi-orthogonal” or even closely coupled with each other, such as the altitude and airspeed capability in the airplane performance envelope example.

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[Ravi Sharma]

Chris and Hans

Both are correct observations.

Any point anywhere is "dynamic" as even the most periodic "electron" orbits never retrace the same location temporally. In addition nature (physics) also assigns probabilities to these space and time combination determination i.e. your geodetic points.

For accurate geodesy these models (and these days realtime digitally updated) need to account for minor mass movements such as rainfall, geology, earthquake and volcano type activities, wht to talk of Tsunami type events!

Finally realtime updation of geoid at or near the point of use.

Regards,

Thanks.

Ravi

(Dr. Ravi Sharma, Ph.D. USA)

NASA Apollo Achievement Award

Former Scientific Secretary ISRO HQ

Ontolog Board of Trustees

Particle and Space Physics

Senior Enterprise Architect

SAE Fuel Cell Standards Member

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[Chris Partridge]

Hi Hans,

Agreed.

We are finding that if one tidies up the ontological foundations then there are a number of simple recurring patterns that explain exactly these kinds of phenomenon. And, as you say, we expose the links between the patterns.

My questions about Null Island was a way of getting the discussion of the ontological foundations in focus.

I think this may be a useful case study for how ontological accuracy helps to tidy up the underlying foundations.

Best,
Chris

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[Ravi Sharma]

Chris

For this to happen, ontologies need to contain all entities and their dynamic variations for the  models to be correct.

For most parts it is classical space and time, unless speeds are measurable fractions of "c".

Thanks.

Ravi

(Dr. Ravi Sharma, Ph.D. USA)

NASA Apollo Achievement Award

Former Scientific Secretary ISRO HQ

Ontolog Board of Trustees

Particle and Space Physics

Senior Enterprise Architect

SAE Fuel Cell Standards Member

To view this discussion visit https://groups.google.com/d/msgid/ontolog-forum/CAMWD8MqOC9fqSyO8%2BKXXnqVspAF_X6DnNYc0jbpTEUhEqHg30A%40mail.gmail.com.

[John F Sowa]

Chris,

  

I agree that examining a wide range of successful applications is always a good way to get started (or perhaps redirected) in any kind of project.

I'd also emphasize that the issue of coordinate systems is at the interface between ontologies and practical application design and development.    Ontology addresses the issue of what exists.  Application development addresses the selection of tools and techniques.    

Coordinate systems are at the interface between them.   The Tesla example showed the need for different coordinate systems for different aspects of the same software system.  The example of a rocket trip to the space station is another example. 

I'm sure that any complex project would require multiple coordinate systems for different aspects.  In building a house, the projects for building the frame, the plumbing, the electrical wiring, the heating system, the air conditioning system, the kitchen, the bathroom, the exterior, the interiors of each room, the basement, the attic, all the equipment, etc., etc., etc.

Just building a single-family home would require multiple coordinate systems.  Imagine the problems of building and equipping a large skyscraper.   Or a large ship, or airplane, or space station, etc

John

 

---

From: "Chris Partridge" <partri...@gmail.com>

Hi John,

WRT: My only point is that the choice of coordinate system depends primarily on the application.  The same basic ontology may be used with an open-ended variety of coordinate systems for different kinds of applications.

Agreed. There is (or should be) a framework or pattern for coordinate systems, that you are able to deploy in whatever application is needed. (As an aside, I think relativity's relative spaces play a part in that framework, in that every coordinate system is based upon a relative space).

The question is, what is that framework or pattern? And, I'm suggesting that we start investigating that by looking at very specific cases. If these turn out to be obvious or trivial, we can move on. If we find they raise questions, we should look into how they are answered.

Chris

On Wed, 18 Feb 2026 at 02:49, John F Sowa <so...@bestweb.net> wrote:

Hans,

I think we agree about what to do and how to do it.

My point is that the choice of coordinate system depends primarily on the application.  The same basic ontology may be used with an open-ended variety of coordinate systems for different kinds of applications.

[Chris Partridge]

Hi Ravi,

Good point.

WRT: For this to happen, ontologies need to contain all entities and their dynamic variations for the  models to be correct.

I think that the way these systems work is to define a practical achievable methodology for tracking position in space at a time (i.e. in spacetime).

They realise that this will not track it exactly, so they calculate and monitor the tolerances. 

In this way they only need the "entities and their dynamic variations" for their practical (idealisation?) model. 

What the ontological work I'm looking at now is doing is helping to characterize their choices. 

If one wanted to ontologise physics work with relativity, then your point would be spot on.

What is interesting in the work I am doing is that some of the basic background framework for relativity (spacetime and relative spaces) maps neatly onto the choices being made.

Chris

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