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Jul 5, 2022, 5:54:37 PMJul 5

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I would like to know if in spatialite you can overlap topologies?

Using the commands: ST_AddIsoNode ST_AddIsoEdge ST_AddEdgeNewFaces

select CreateTopology('oneT',2180,0,0)

I created a geometry that is topologically correct inside oneT topology

select CreateTopology('secondT',2180,0,0)

Using the commands: ST_AddIsoNode ST_AddIsoEdge ST_AddEdgeNewFaces

I created a geometry that is topologically correct inside secondT topology

Is there a command that intersects these two geometries (two topologies) oneT with secondT topology?

Regards,

Artur K,

Jul 6, 2022, 2:31:32 AMJul 6

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I'm not really sure to understand your question.

You apparently seem to assume that a "topology" is the

equivalent of a "geometry", but this is conceptually wrong.

a "topology" is a complex set of many Node, Edge and Face

primitives ... may well be millions and millions of them.

determining the intesections between two different Topologies

is consequently a nonsense.

what you probably mean is to get a topological set of

many different individual "geometries" wich could may

be have reciprocal intersections between them.

in this case you simply have to create just a single

Topology then inserting all your "geometries" into it.

you can use SQL functions such as TopoGeo_AddPoint()

[for POINT geometries] and/or TopoGeo_AddLineString()

[for LINESTRING or POLYGON-RING geometries]; both

functions accept a single geometry at each time.

even better, you can directly call TopoGeo_FromGeoTable()

[note that there are several flavours of it] in order

to directly transform a full layer of "geometries"

into a corresponding Topology.

in any case the dirty work of identifying all intersections

and overlaps transforming all them in a Topological coherent

set of Nodes, Edges and Faces will be silently performed as

required in the most painless way.

bye Sandro

Jul 6, 2022, 3:41:15 AMJul 6

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Hi Sandro,

Thank you very much for your reply. Unfortunately, I didn't fully understand it - and I learned about new things that I can't understand.

Therefore, let me divide the question into two parts.

1) First - Two topologies

tplot - A large number of plots (or parcels) in some county, dozens or even hundreds of plots - a lot of nodes, borders and faces (existing objects)

troad - the geometry of the road being designed (this is just a plan - but there is a precision geometry specified for this project for this county)

I do not want to mix the geometry of the plots with the geometry of the designed road.

I would like to use the function to intersect these two topologies between themselves.. Is it possible to perform such operations on these topologies?

2) Second "TopoGeo_FromGeoTable()"

Sorry but only yesterday I read something about the "TopoGeo_FromGeoTable()" function and I do not fully understand the concept of how this function works.

Using this function "TopoGeo_FromGeoTable()" can I turn geometry from "tplot" (node-border) into geometry - polygon (WKB)?

If so, further analysis I can use ST_Intersection function.

Artur K,

Jul 6, 2022, 4:40:54 AMJul 6

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On Wed, 6 Jul 2022 09:41:00 +0200, Artur Krawczyk wrote:

> Therefore, let me divide the question into two parts.

> 1) First - Two topologies

>

> Therefore, let me divide the question into two parts.

> 1) First - Two topologies

>

> tplot - A large number of plots (or parcels) in some county, dozens

> or even hundreds of plots - a lot of nodes, borders and faces

> (existing objects)

> troad - the geometry of the road being designed (this is just a plan

> - but there is a precision geometry specified for this project for

> this county)

> I do not want to mix the geometry of the plots with the geometry of

> the designed road.

>

> I would like to use the function to intersect these two topologies

> between themselves.. Is it possible to perform such operations on

> these topologies?

>

absolutely NO. full stop.
> or even hundreds of plots - a lot of nodes, borders and faces

> (existing objects)

> troad - the geometry of the road being designed (this is just a plan

> - but there is a precision geometry specified for this project for

> this county)

> I do not want to mix the geometry of the plots with the geometry of

> the designed road.

>

> I would like to use the function to intersect these two topologies

> between themselves.. Is it possible to perform such operations on

> these topologies?

>

a Topology is a self constrained Universe; comparing it in

any way with another different Topology has no sense at all.

"intersection" requires Geometries and not Topologies.

What you can do is:

1) transform both topologies into ordinary Geometry-based

tables (e.g. by calling TopoGeo_ToGeoTable)

2) then calling ST_Intersects() for indentifying all possible

intersection between the two "geom-tables" deriving from

the previous step.

> 2) Second "TopoGeo_FromGeoTable()"

>

> Sorry but only yesterday I read something about the

> "TopoGeo_FromGeoTable()" function and I do not fully understand the

> concept of how this function works.

>

> Using this function "TopoGeo_FromGeoTable()" can I turn geometry from

> "tplot" (node-border) into geometry - polygon (WKB)?

>

and native binaries geometries of SpatiaLite, that are a different

thing.

TopoGeo_FromGeoTable() works exactly in the opposti way;

it transforms a whole Geometry-Table into a corresponding

Topology.

For transforming a Topology into a corresponding Geometry-Table

you should call instead TopoGeo_ToGeoTable().

> If so, further analysis I can use ST_Intersection function.

>

the only two SQL functions intended for identifying any

possible intesection between geometries.

but they only accept Geometries and not Topologies.

said in different words:

a) a first conceptual model is the one based on OGC

Geometries (Points, Linestrings, Polygons etc)

b) a second conceptual model is the one based on ISO

Topologies, that implies a completely different

approach.

you can never mix the one with the other because they

are mutually not compatible.

what you can do is to transform Geometries into

Topologies or Topologies into Geometries, in such

a way as to correctly compare apples with apples

and oranges with oranges.

by Sandro

Jul 6, 2022, 6:21:45 AMJul 6

to spatiali...@googlegroups.com

> Therefore, let me divide the question into two parts.

> 1) First - Two topologies

>

> tplot - A large number of plots (or parcels) in some county, dozens

> or even hundreds of plots - a lot of nodes, borders and faces

> (existing objects)

> troad - the geometry of the road being designed (this is just a plan

> - but there is a precision geometry specified for this project for

> this county)

> I do not want to mix the geometry of the plots with the geometry of

> the designed road.

>

> I would like to use the function to intersect these two topologies

> between themselves.. Is it possible to perform such operations on

> these topologies?

>

absolutely NO. full stop.

a Topology is a self constrained Universe; comparing it in

any way with another different Topology has no sense at all.

"intersection" requires Geometries and not Topologies.

What you can do is:

1) transform both topologies into ordinary Geometry-based

tables (e.g. by calling TopoGeo_ToGeoTable)

2) then calling ST_Intersects() for indentifying all possible

intersection between the two "geom-tables" deriving from

the previous step.

Thank you Sandro for such an extensive explanation now I understand why this transition between TopoGeo_ToGeoTable and back TopoGeo_FromGeoTable()

More or less job will be like this:

tplot topology table -> TopoGeo_ToGeoTable -> tplotGT (Geotable)

troad topology table -> TopoGeo_ToGeoTable -> troadGT (Geotable)

CREATE TABLE pintGT .......... ST_Intersection ( tplotGT,troadGT )

tinter a topology from - TopoGeo_FromGeoTable(pintGT)

tinter - topology table as a result of intersection ;-)

Best Regards,

Artur K,

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