[Qgis-developer] Raster resampling

[Radim Blazek]

On Tue, Jan 17, 2012 at 1:32 PM, Marco Hugentobler
> The problem here is that resampling sometimes can only be done once you know
> the pixel color. E.g. in case of paletted raster, two adjacent pixel values
> can have totally different color (therefore resampling needs to be done on
> color components, not on raster value).

OK.

> How is it with GRASS? it probably has the resampling on a lower level?

GRASS supports  only nearest neighbour.

>> I am especially concerned about reprojection, because reprojection of
>> images oversampling^2 times bigger may be significantly slower.
>
>  True, I need to do some more tests here. At the moment, the oversampling
> rate is kept at a maximum of 4 (that should probably be a user option
> later). Ok, maximum 16 times more data to reproject (hopefully no problem
> with your approximative reprojection :-) ).

It seems that sometimes it is slower reprojection and sometimes
resampling, depending on which resampling algorithm is used,
complexity of projection and if approx repro is used. We need some
benchmarks on this. Would it be possible to have an optional order of
projection and resampling and choose the faster one on runtime?

Radim