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

[Peter Baumann]

On 11/03/2017 08:57 AM, Ari Jolma wrote:
> I have two things that I need to ask/discuss regarding WCS 2.0
>
> 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. 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.
>
> 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) 

that is correct, Ari

> in the dataset definition (WCS_GDAL XML). Thus GDAL needs to show the coverage
> bbox to its users in that CRS. 

no, it's just one bbox; WGS84 is common. Otherwise you'd have to advertise
sometimes thousands of bbox variants, which is not feasible.
-Peter

> And, as above, the GeoTransform is east-north.
>
> Is this correct analysis?
>
> BTW, the coordinate transformation of the bbox is not done in WCS driver at
> the moment in the case of user CRS != server native CRS.
>
>
> 2) WCS can offer multidimensional data with complex data records. I want the
> GDAL user to have a control on how the data is organized into (current) GDAL.
> For example the server may offer spatio-temporal (x/y/t) data with about wave
> heights in a sea (to link this to what I'm getting paid for now :)) that are
> described as average and max. Obviously I want x/y bands, but I may want
> either the temporal data or the wave height data into bands, depending on the
> application. The workflow would go
>
> 1. gdalinfo to the server, see this data as a layer with name
> "VHM0_year_meanmax", gdalinfo reports that layer as a subdataset
>
> 2. gdalinfo into the layer, now it reports that there is an additional
> dimension (t) and that the datarecord consists of two values mean and max; it
> also reports information about the time (begin, end, step)
>
> 3. I decide to use a specific time and start using datasets with two bands
> (mean and max)
>
> I have such data as NetCDF and I don't think I can follow that workflow with
> it since the driver puts the mean and max wave heights right away into
> subdatasets and time into bands.
>
> In the WCS there could/should be a similar default behavior but that should be
> changeable by options (-oo t=some_timestamp).
>
> Thoughts?
>
> Ari
>
>
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-- 
Dr. Peter Baumann
 - Professor of Computer Science, Jacobs University Bremen
   www.faculty.jacobs-university.de/pbaumann
   mail: p.baumann at jacobs-university.de
   tel: +49-421-200-3178, fax: +49-421-200-493178
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