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

[Ari Jolma]

one detail forgotten

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.

There is also the coverageFunction, which contains, in the case of 
grids, a GridFunction. GridFunction may contain non-Linear sequenceRules 
but they are probably too exotic to be supported by the GDAL WCS driver.

>
> 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
>
>