[gdal-dev] Warping quality with small geolocation arrays

[Knut-Frode Dagestad]

Dear list,

Warping datasets with geolocation arrays works fine if the arrays have 
the same size as the other raster bands. However, if the geolocation 
arrays are much smaller, the quality is very bad.

Say I have a 2000x2000 px dataset with 100x100 px sized geolocation 
arrays. Then a warped image have only 200x200 blocks of identical 
values, even if the size of the warped image is much larger. If I change 
the interpolation algorithm (neareast, cubic...) the values change 
slightly, but the real output resolution remains low. This is the same 
whether using Python API or gdalwarp. As a workaround I convert the 
geolocation arrays to GCPs. This gives decent warping quality, but is a 
bit awkward.

Is this the expected behavior of the present implementation of 
geolocation arrays in GDAL?

Best regards from Knut-Frode