[GRASS-dev] bilinear and bicubic raster interpolation

[Hamish]

Markus Metz wrote:
> In i.rectify, I have implemented the interpolation methods available
> in r.proj, and while testing discovered an offset of one cell (row +
> 1, col + 1 from source to target) between the source and target
> imagery after rectifying (40+ automatically collected GCPs, order=1,
> sub-pixel RMS errors, source image not distorted). I corrected this
> offset in i.rectify and suggest that all modules using
> Rast_interp_linear/Rast_interp_bilinear/Rast_interp_cubic/Rast_interp_bicubic
> should be checked. I am pretty sure that at least r.proj needs this
> fix (if a one-cell shift is something to worry about).

For MODIS satellite data the cells can be 4km tall, for GRIB data 1/2 degree
or full degree. So once reprojected from eg lat/lon to UTM, the cells are
still quite big and a 1 cell offset can be significant when trying to
ground-truth against in situ measurements.

also, i.rectify and gdalwarp share the same code source for order= matrix
calcs, so maybe we should check for the same there if that was touched.


thanks,
Hamish