[gdal-dev] gdalwarp: question about methods implemented when source grid is denser than target.

[Even Rouault]

Hi,

to briefly answer your question, for the methods bilinear, cubic, 
cubicspline and lanczos who have nominal kernel radius of respective 
values 1, 2, 2 and 3 (and thus a diameter double that size), the radius 
is extended by a factor source_size / dest_size to take into account the 
downsampling ( Cf lines 1188-1195 in alg/gdalwarpkernel.cpp), and the 
weights of the resampling kernel are evaluated with a scale factor too 
(cf lines 3713-3715 / 3741-3743)

Even

Le 24/05/2023 à 16:29, Ramiro Espada Guerrero a écrit :
> Hi,
>
> I would like to know if gdalwarp does any "average" regriding when the 
> source grid is denser than the target grid regardless of the chosen 
> method for the interpolation. And if there is any document where I can 
> follow exactly the calculations. I tried to follow the code on github 
> but it is pretty difficult to follow.
>
> I've programmed my own bilinear interpolation function in fortran and 
> I got smoother results when I applied -r bilinear with gdalwarp. So i 
> wonder if there is a pre-average regriding subroutine that is not in 
> the documentation page.
>
> Thanks!
>
>
>
>
>
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