[Requests] OGC Web Coverage Service - Transaction operation extension - Comment

Simon.Cox at csiro.au Simon.Cox at csiro.au
Wed Aug 5 17:56:00 EDT 2015


Ø  Therefore, we have prepared a WCS Extension which I want to propose for voting at the Nottingham TC. This extension introduces a very simple concept: an XPath expression can be submitted which is evaluated on the Capabilities document on server side. This allows applications to get exactly what they need, without excess data transfer. If you feel that this is a way forward, maybe you want to support this in the upcoming TC meeting - any such support is greatly appreciated!

And perhaps better still, submit this idea as an OWS Common CR or as input to the upcoming revision.

From: Requests [mailto:requests-bounces+simon.cox=csiro.au at lists.opengeospatial.org] On Behalf Of Peter Baumann
Sent: Wednesday, 5 August 2015 5:31 PM
To: Timothy Astle <timothy.astle at caris.com>; requests at lists.opengeospatial.org
Subject: Re: [Requests] OGC Web Coverage Service - Transaction operation extension - Comment

Dear Timothy,

after completion of the RFC period I'm coming back to your (very thoughtful) questions below.

Re Req 8: This actually is a known issue with OWS Common. A service provider can decide which elements to expose in a Capabilities document, which has been considered sufficient in the past. Alas, it does not solve the issue - practice shows that either you get not enough information, or too much (such as all coverages listed). In fact, the Capabilities mechanism is way too static and inflexible.

OGC has started thinking about how to fix and modernize, but there is no relief on the horizon soon. Therefore, we have prepared a WCS Extension which I want to propose for voting at the Nottingham TC. This extension introduces a very simple concept: an XPath expression can be submitted which is evaluated on the Capabilities document on server side. This allows applications to get exactly what they need, without excess data transfer. If you feel that this is a way forward, maybe you want to support this in the upcoming TC meeting - any such support is greatly appreciated!

Re References to grids: Core and extensions have been formulated very carefully so as to allow all coverage types defined, which includes point clouds and meshes. Currently, there is one extension which specifically refers to grids, that is WCS Scaling: change of resolution is an operation meaningful on grids only (at least that is my current understanding). Concretely speaking about WCS-T, a point cloud (MultiPointCoverage) or mesh (MultiCurveCoverage or MultiSurfaceCoverage or MultiSolidCoverage) can be inserted and deleted, and can even be updated. Of course, update of a mesh requires more complex consistency constraints to be respected, but that is inherent to the definition of such mesh types, so does not have to be treated separately here.

Actually, there is nothing in the mask parameter that confines us to a grid. Consider a point cloud, for example, The mask in this case will contain the direct positions of the points to be updated, associated with a range value of "1" (likely in this case the "0" points will simply be left out), and this guides the server on the points to be updated - say, with a new temperature value. Hence, I'd claim that this definition works on all coverage types - kindly let me know should I miss something here, it's a good opportunity to catch any and all hiccups.

And obviously there is one: searching for the root cause of your concern I find occurrences of "maskGrid", a leftover forgotten in an earlier renaming action. I have corrected this, and it actually resolves an inconsistency - good catch!

Thank you again for the encouraging assessment and your thoughtful comments. Looking forward to further discussion in future.

best regards,
Peter

On 2015-06-26 20:48, Timothy Astle wrote:
A couple of questions:

Requirement 8
After completion of a successful InsertCoverage request, the identifier of the coverage established in the server’s offering shall be listed as an existing coverage in this WCS service’s Capabilities document.

OGC 06-121r9 (OGC Web Services Common Standard) still allows for the idea of an "otherSource" for finding OWS content.  Is the above requirement mandating that when implementing a WCS-T, you must describe the coverage in the Capabilities' CoverageSummary list?  I'm concerned that when dealing with a large amount of coverages, that could really degrade the performance of a system.

References to Grids

I definitely see value to this transactional extension to WCS.  I'm definitely interested to watch WCS grow beyond gridded data.  In this particular extension, I see references to grids and grid-related terminology and concepts.  I'm concerned that if / when point clouds or TINs are introduced as extensions, that this specification might not make sense in some contexts.  For example, if a WCS was created that specialized in TINs, the optional grid parameters wouldn't really apply.  Is the intent that this is a "grid transactional operation extension" or a "general coverage operation extension"?  Would a future point cloud transactional extension be created for point cloud operations?  I guess I'm just asking for clarification.

Thank you for your time and consideration.
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Dr. Peter Baumann

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