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

Tue Nov 7 06:29:42 PST 2017

Ari-

On 11/07/2017 09:56 AM, Ari Jolma wrote:
> Thanks for the replies before. I believe I'm getting closer, but slowly.
>
> In my earlier question I was referring to three CRSs. I now believe that it is
> only two since I had overlooked requirement 23, which to my understanding
> requires that the CRS of the coverage (top level boundedBy element) is the
> same as the CRS of the grid (in domainSet element). Thus GDAL can and should
> set the dataset size and geotransform by what's in domainSet and there's no
> such ambiguity in the grid size as I thought.
>
> To get multidimensional data into GDAL 2D domain, one may need to slice the
> data at some point in the non x/y dimensions. I'm testing this with the
> Rasdaman server. My code currently creates a KVP
> "SUBSET=unix(2008-01-08T00:02:58.000Z)" in an attempt to slice the time
> dimension. The whole test URL is
>
> http://ows.rasdaman.org/rasdaman/ows?SERVICE=WCS&REQUEST=GetCoverage&VERSION=2.0.1&COVERAGEID=test_irr_cube_2&FORMAT=application%2Foctet-stream&SUBSET=E(75042.7273594,95042.7273593873)&SUBSET=N(5434865.55794,5454865.55794)&SUBSET=unix(2008-01-08T00:02:58.000Z)&RANGESUBSET=b1
>
>
> which replies
>
> Trimming subset in WCS must follow this syntax 'lowerBound,upperBound', given
> '2008-01-08T00:02:58.000Z'.

did you try putting the time string in double quotes? As the string can have any
syntax it needs to be escaped.

>
> I don't understand why. I'm trying to slice, not trim. I don't know of other
> servers serving >2D data so I can't test with other brands.

syntactically, you are slicing because you have only one time coordinate;
trimming needs lower + upper bound.

-Peter

>
> With a MapServer instance I have a problem setting the rangesubset, it does
> not seem to work with field names, only indexes.
>
> http://194.66.252.155/cgi-bin/BGS_EMODnet_bathymetry/ows?SERVICE=WCS&REQUEST=GetCoverage&VERSION=2.0.1&COVERAGEID=BGS_EMODNET_CentralMed-MCol&FORMAT=image%2Ftiff&SUBSET=long(9.83125,9.83958334)&SUBSET=lat(46.18124999,46.18958333)&RANGESUBSET=band1
>
>
> does not work although band1 is given as name in coverage description, but
>
> http://194.66.252.155/cgi-bin/BGS_EMODnet_bathymetry/ows?SERVICE=WCS&REQUEST=GetCoverage&VERSION=2.0.1&COVERAGEID=BGS_EMODNET_CentralMed-MCol&FORMAT=image%2Ftiff&SUBSET=long(9.83125,9.83958334)&SUBSET=lat(46.18124999,46.18958333)&RANGESUBSET=1
>
>
> works.
>
> Ari
>
>
> Ari Jolma kirjoitti 03.11.2017 klo 09:57:
>> 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) 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?
>>
>> 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
 - Executive Director, rasdaman GmbH Bremen (HRB 26793)
   www.rasdaman.com, mail: baumann at rasdaman.com
   tel: 0800-rasdaman, fax: 0800-rasdafax, mobile: +49-173-5837882
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