[gdal-dev] Warp with different band types?

[Even Rouault]

Le 25/08/2021 à 13:12, Idan Miara a écrit :
> Thanks Even!
>
> For my case, max(data types) is good enough, but I see that for the 
> general case calling this function might be a better option.
>
> I couldn't find a reference for GDALWarpResolveWorkingDataType in the 
> python wrappers, or the warp tester:
> https://github.com/OSGeo/gdal/blob/master/autotest/alg/warp.py 
> <https://github.com/OSGeo/gdal/blob/master/autotest/alg/warp.py>
It's not meant for general consumption. Mostly an implementation detail
>
> Looking at 
> https://github.com/OSGeo/gdal/blob/master/autotest/cpp/test_alg.cpp#L89 
> <https://github.com/OSGeo/gdal/blob/master/autotest/cpp/test_alg.cpp#L89>
> I couldn't find a test that is considering two bands with different 
> data types.
>
> I was expecting that, at least in the python version, gdal.Warp will 
> call this function internally before warping and not take the first 
> data type as a default.
gdal.Warp() just calls the same logic as the gdalwarp binary. The fix 
shouldn't be too hard if you want to have a try. Otherwise please file a 
ticket about that
>
> Idan
>
> On Mon, 23 Aug 2021 at 11:51, Even Rouault <even.rouault at spatialys.com 
> <mailto:even.rouault at spatialys.com>> wrote:
>
>     Idan,
>
>     The warping kernel works on a multiple band dataset by using a
>     single working data type, which should be the "max" of the types
>     of the input bands, so here int16. I believe this is working, but
>     here the issue is more at the creation of the dataset itself than
>     during the warping. This is due to
>     https://github.com/OSGeo/gdal/blob/3302b5c9cb62191df3409676aa97fced07c92c3b/gdal/apps/gdalwarp_lib.cpp#L3017
>     <https://github.com/OSGeo/gdal/blob/3302b5c9cb62191df3409676aa97fced07c92c3b/gdal/apps/gdalwarp_lib.cpp#L3017>
>     . GDALWarpResolveWorkingDataType() should likely be used instead
>
>     Even
>
>     Le 23/08/2021 à 00:58, Idan Miara a écrit :
>>     Hi all,
>>
>>     I was trying to warp a ds with a byte band and an int16 band and
>>     got a ds with two byte band.
>>     Is warp using the first band data type for all the output bands?
>>     Is that a bug?
>>
>>     If multiple band types are not supported - maybe max(band types)
>>     could be a better default (assuming no explicit output type) ?
>>
>>     Kind regards,
>>     Idan
>>
>>
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>
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