On the possible extension of PDAP for complex Geometrical queries

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Pedro Osuna

Jul 7, 2011, 9:54:32 AM7/7/11
to ipda...@planetarydata.org, dapwg, Steve Hughes, Sean Kelly, Yukio Yamamoto, Dan Crichton, ipda...@googlegroups.com
Dear all,

(note I am unsure of email lists and their contents, thus I send to many recipients; will have to check in order to avoid unnecessary duplications in the future)

Following our recent meetings and suggestions (e.g., from EuroPlanet colleagues, JAXA colleagues, etc.), Jesús and myself are looking into the problem of how to expand the PDAP capabilities in order to be able to handle complex geometrical queries.

While looking into that, the very first issue we face is the absence of clear Use Cases as to what we are aiming to solve when trying to expand the PDAP capabilities for Geometrical searches. 

In order to help to clarify what I mean, let me describe what I consider might be a use case that eventually would need to be solved using PDAP (note it is a completely fictious and fake example with even possibly wrong keywords):

Use Case: "Find data on Mars from four different missions (1 NASA Orbiter, 1 ESA orbiter, 1 JAXA Rover, 1 mission during a FlyBy over Mars) over region of interest bounded by maximum circles around longitude between 35 and 40 degrees and latitude between 25 and 30 degrees"

The idea of this use case would be to send _the same PDAP query_ to four different PDAP services running at, let's say, NASA, ESA, JAXA and EuroPlanet sites. The eventual query would look like:

Where we have "forced" the query to all the four different servers to search into their datasets using Mars-centered Planetocentric spherical coordinates.

Now, let's say that the data in the different servers are in the following formats:

- NASA Orbiter: Planetographic Mars centered coordinates  (PDS keyword for COORDINATE_SYSTEM_NAME=PLANETOGRAPHIC)
- ESA Orbiter: Planetocentric Mars centered coordinates   (PDS keyword for COORDINATE_SYSTEM_NAME=PLANETOCENTRIC)
- EP FlyBy mission:   Non rotating spin coordinates (PDS keyword for COORDINATE_SYSTEM_NAME=NON-ROTATING SPIN COORDINATES)

Now, the four different servers would have to:

1) transform the input coordinates (in Mars planetocentric spherical) to their own coordinates
2) execute their query internally
3) transform their internal coordinate system back to the Mars planetocentric to give the results

This does not look an easy task to do. In my understanding, one of the few ways to do this is by using the SPICE kernels internally for each of the missions and using the SPICE libraries to convert from one system to another. While this is a possibility, I understand it is not an easy task at all.

The above example is only using one or two of the available Geometrical PDS keywords. There are many others (up to 146) that could be used in order to be able to do complete and complex geometrical queries, see:

While the PDAP could be made flexible enough to accommodate any of those keyword queries, it looks like there would be very few clients able to transform the queries from one system to another unless they use the SPICE data and libraries, which seems a very complex exercise.

One could think of a way to introduce the SPICE data as part of the possible "entities" to be searchable by the PDAP, but I strongly believe this would overcomplicate the whole picture enormously and might not be worth the effort.

Therefore, and without going any further, I think the single most important issue that we have to figure out and discuss is:

- Do we really _need_ to expand the PDAP as is today to accommodate more complex Geometrical queries?
- Would it be feasible (from the server _and_ client point of view) to implement the necessary transformations?

And the single most important question:

- Which are the Use Cases calling for an extension of the PDAP for Geometry handling (and do they fit in the aforementioned two main questions?)

Following this, I think it would be of utmost importance to have a set of Use Cases that would determine the necessity of extending PDAP in this sense.

Could you then, please, write the SET OF USE CASES that you would consider from your agency's point of view as cases that would require PDAP extension?

They should be accompanied by as much information as possible (in terms of PDS keywords, coordinate systems, science to be extracted from the use case, etc., etc.)

It would be interesting to have this information as soon as possible so we can think over it during the hardly two months there are before the September IPDA meeting, so please send your information as soon as possible.

Wait for your news.

Pedro Osuna Alcalaya

European Space Agency (ESA)
European Space Astronomy Centre (ESAC)
Science Operations Department (SRE-O)
Science Archives and Computer Support Engineering Unit (SRE-OE)
European Space Astronomy Centre (ESAC)
P.O. Box 78
E-28691 Villanueva de la Cañada

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