[mapserver-dev] WCS 2.0 support and specification compliance

[Fabian Schindler]

Hi Andrea,

You are right, in the current msautotest suite there are several tests 
and examples that are not (yet) standardized. The "problem" with the 
current version of WCS is that it follows a core+extensions approach, 
which is not a problem by itself, it just makes a useful implementation 
quite difficult. To provide features for WCS 2.0 that are also available 
for older versions of the standard we simply had to make educated 
guesses on what is likely to be standardized in future extensions. For 
example the "formats" extension was not available at all when I 
implemented it in MapServer, but when the standard was finished, only 
small changes had to be applied to be conformant to the extension.

In the current documentation you'll find a note [1] for what I just 
explained.

In the specific example of the "crs" parameter in the "wcs:Dimension" 
element, I think you have stumbled upon an inconsitency and the test 
input/documentation needs to be updated.

Currently the "scaling" extension for WCS 2.0 is under discussion at the 
OGC WCS standards working group, and, once it is standardized, the 
"Size" and "Resolution" will likely have to be adjusted. (With the 
current state of the document, they will be replaced by the 
"scaleFactor", "scaleAxes" and "scaleDomain" parameters). I think the 
standard document is not publicly available, only in the OGC internal 
system.

Thank you for the hint of putting the parameters into the 
"wcs:Extension" element. This was a recent change in the corrigendum 
that may not have been taken into account in the implementation.

Regards,
Fabian


[1] 
http://mapserver.org/ogc/wcs_server.html#to-do-items-and-known-limitations


On 08/17/2012 02:24 PM, Andrea Aime wrote:
> Hi all,
> sorry to intrude on the MapServer dev mailing list, but I'd have a 
> question that
> only the people that implemented the WCS 2.0 support could answer.
>
> I see that the MapServer autotest has requests that comprise 
> parameters which
> are not part of the official specification, which add support for 
> scaling and reprojection.
> For example:
>
> <?xml version="1.0" encoding="UTF-8"?><wcs:GetCoverage 
> xmlns:wcs="http://www.opengis.net/wcs/2.0" service="WCS" 
> version="2.0.0"><wcs:Format>image/tiff</wcs:Format><wcs:CoverageID>grey</wcs:CoverageID><wcs:DimensionTrim><wcs:Dimension 
> crs="http://www.opengis.net/def/crs/EPSG/0/4326">lon</wcs:Dimension><wcs:TrimLow>-121.488</wcs:TrimLow><wcs:TrimHigh>-121.487</wcs:TrimHigh></wcs:DimensionTrim><wcs:DimensionTrim><wcs:Dimension 
> crs="http://www.opengis.net/def/crs/EPSG/0/4326">lat</wcs:Dimension><wcs:TrimLow>0.000</wcs:TrimLow><wcs:TrimHigh>0.001</wcs:TrimHigh></wcs:DimensionTrim></wcs:GetCoverage>
>
> (the Dimension element does not have a crs attribute in the official 
> spec).
>
> <?xml version="1.0" encoding="UTF-8"?><wcs:GetCoverage 
> xmlns:wcs="http://www.opengis.net/wcs/2.0" service="WCS" 
> version="2.0.0"><wcs:Format>image/tiff</wcs:Format><wcs:CoverageID>grey</wcs:CoverageID><wcs:Size 
> dimension="x">10</wcs:Size><wcs:Size 
> dimension="y">20</wcs:Size></wcs:GetCoverage>
> or
> <?xml version="1.0" encoding="UTF-8"?><wcs:GetCoverage 
> xmlns:wcs="http://www.opengis.net/wcs/2.0" service="WCS" 
> version="2.0.0"><wcs:Format>image/tiff</wcs:Format><wcs:CoverageID>grey</wcs:CoverageID><wcs:Resolution 
> dimension="x">20</wcs:Resolution><wcs:Resolution 
> dimension="y">20</wcs:Resolution></wcs:GetCoverage>
>
> (there is no Size and Resolution element in the specification)
>
> The WCS 2.0 specification says that the scaling, interpolation, band 
> subsettting and reprojection should have been
> addressed by application profiles that, to date, have not been 
> released, but my understanding is that in POST
> requests these extra things would have to be added inside the 
> wcs:Extension element.
>
> I also see there is a KVP syntax for them in MapServer.
>
> Long story short, I'm wondering, where is the above coming from? Is it 
> educated guesses from the MapServer
> developers, or coming from documents that OGC never released (or that 
> yours truly simply did not find?).
> I also looked in other software (Rasdaman) and there is apparently no 
> trace of handling these extra parameters
>
> Cheers
> Andrea
>
>
> _______________________________________________
> mapserver-dev mailing list
> mapserver-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapserver-dev

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