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

Joshua Lieberman jlieberman at tumblingwalls.com
Thu Aug 6 13:52:17 EDT 2015


The Capabilities as Catalog idea is pretty old (2003 at least), but there may finally be a critical need to move in that direction.

Josh

> On Aug 6, 2015, at 1:06 PM, Timothy Astle <timothy.astle at caris.com> wrote:
> 
> I like the idea of leaning on an existing API, like OpenSearch or a CSW.  Both would work.  This is what I imagined what the OWS Common "OtherSource" was designed for.  I find using an existing API is a nicer approach than creating something new.  (Similar to Tim Bray's "Don't Invent XML Languages <http://www.tbray.org/ongoing/When/200x/2006/01/08/No-New-XML-Languages>" adage.)
> 
> Tim
> 
> On 06/08/2015 1:36 PM, Panagiotis (Peter) A. Vretanos wrote:
>> Simon at al. 
>> 
>> Already done ... but we used an OpenSearch API rather than XPath letting the underlying server pick nay query technology it likes. 
>> 
>> https://portal.opengeospatial.org/files/?artifact_id=54580 <https://portal.opengeospatial.org/files/?artifact_id=54580> 
>> 
>> Ciao. 
>> 
>> On 08/05/2015 05:56 PM, Simon.Cox at csiro.au <mailto:Simon.Cox at csiro.au> wrote: 
>>> ØTherefore, 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 <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> <mailto:timothy.astle at caris.com>; requests at lists.opengeospatial.org <mailto: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 thatwhen 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 seereferences to gridsand grid-related terminology 
>>>     and concepts.  I'm concerned that if / when point clouds or TINsare 
>>>     introduced as extensions, that this specification might not makesense 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. 
>>> 
>>>     -- 
>>> 
>>>     Tim Astle 
>>>     Development Manager for Web Technologies 
>>> 
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>>> 
>>> -- 
>>> 
>>> Dr. Peter Baumann 
>>> 
>>>   - Professor of Computer Science, Jacobs University Bremen 
>>> 
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>> 
> 
> -- 
> Tim Astle
> Development Manager for Web Technologies
> 
> CARIS <http://www.caris.com/>
> 115 Waggoners Lane
> Fredericton, New Brunswick
> Canada    E3B 2L4
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