[gdal-dev] Source pixels used when warping using cubic resampling
Gregory, Matthew
matt.gregory at oregonstate.edu
Fri Nov 15 17:01:36 PST 2019
Hi Even,
Even Rouault wrote:
> > Hi all,
> >
> > I am warping and upsampling an image from 4km to 30m using cubic resampling.
> > I've been warping different sized windows from the source image like this:
> >
> > [snip]
>
> maybe try to add
>
> -et 0
>
> and/or
>
> -wo XSCALE=133.33333333333334 -wo YSCALE=133.33333333333334
>
> where 133.3333 = 4000 / 30
>
> XSCALE/YSCALE are "un-documented" there:
> https://github.com/OSGeo/gdal/blob/master/gdal/alg/gdalwarpkernel.cpp#L1120
Wow, thanks for this - would have never figured this out on my own. For me, both -et and the two -wo flags were necessary to make the reprojections from the full window and the row be equivalent.
Using the -wo flags on their own gets pretty close (~0.5% percent difference in pixel values in my test), but -et on its own was still substantially different (~7% percent differences in pixel values).
thanks, matt
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