[GRASS-user] reprojection problem

[Maciej Sieczka]

Hi,

The unexpected shift after re-projection might be due to
your input Earth model being a sphere, and the output an
ellipsoid. PROJ.4 FAQ has an explanation [1] (the "Changing
Ellipsoid / Why can't I convert from WGS84 to Virtual Earth
Mercator?" part). Shortly put it is about using
"+nadgrids=@null" properly.

I don't know whether GRASS supports nadgrids=@null though.
Try adding it into the projection definition file
(location/PERMANENT/PROJ_INFO) and see if *.proj commands
honour this. Please let us know if it worked.

If this fails, you can re-project rasters outside GRASS,
using gdalwarp. This tool is proven to accept +nadgrids=@null.

Sidenote - I'd suggest to reproject the lat/long data into
LAEA, not the other way round. And propably it would better
to actually re-project both datasatets into LAEA based on an
ellipsoid (WGS84) instead of a sphere.

Maciek