[gdal-dev] downsampling geotiff with a low-pass filter

[Even Rouault]

> Upsampling is well
> covered: cubicspline and lanczos are reasonably sophisticated upsampling
> filters,

Did you actually try them for downsampling ? They are for sure widely used in 
that case already, for example when using gdaladdo to create overviews. For 
example cubicspline has a filter radius of 2. If you downsample by a factor of 
X, the effective radius will be 2 X.

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