[gdal-dev] WCS 2.0, getting (multidimensional) data

Even Rouault even.rouault at spatialys.com
Fri Nov 3 02:07:33 PDT 2017


> 1) My understanding is that there are potentially three CRS in
> operation: the CRS of the bbox of the coverage (the native CRS of the
> server); the CRS of the grid; and the CRS where the user wants the data.
> I can imagine that it is perfectly possible for a server to advertise
> data from an area bounded by geographic coordinates, and that the data
> is in some specific projected coordinate system.

For me the "native" CRS (as much as a client can see) is the one of the 
CoverageDescription.boundedBy.Envelope at srsName attribute. If the server advertizes it as 
EPSG:4326, but the native data is in something else, this is an implementation detail of the 
server. That said, as you mention, the user could then decide to request in that alternative 
CRS if it has knowledge of that.

> Also, the data could be
> regular but not east-north (it is rotated for example). This would be
> described in a CoverageDescription. Despite the rotation, GDAL would
> show the data east-nort (without rotation), since only the bbox of the
> coverage is given.

You should be able to retrieve the rotation/shearing terms in the 
domainSet.RectifiedGrid.offsetVector 's element similarly to other WCS versions

Regarding GridFunction, there was a thread about this some time ago:
 https://lists.osgeo.org/pipermail/gdal-dev/2017-April/thread.html#46366

> 
> Again, it is perfectly possible that the user wants the data in some CRS
> that is not the native CRS of the WCS. The GetCoverage request can
> contain an instruction for the server to serve the data in the CRS the
> user wants the data (this is an extension in 2.0). User can set this (it
> must be one of those supported by the server) in the dataset definition
> (WCS_GDAL XML). Thus GDAL needs to show the coverage bbox to its users
> in that CRS. And, as above, the GeoTransform is east-north.
> 
> Is this correct analysis?

Yes, one could image a user specifying something like
WCS:http://blaba&CRS=something to ask for server reprojection, and the geotransform 
exposed to the user should be in that CRS for consistency.

> 
> 2) [...]
> In the WCS there could/should be a similar default behavior but that
> should be changeable by options (-oo t=some_timestamp).

Sounds reasonable.

Even

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