[Gvsig_english] problems with on-the-fly projection

[Moritz Lennert]

Hello,

I have some trouble with on-the-fly projection: using gps data coming in
WGS84 (epsg 4326) and a topographic map in Belgian Lambert (epsg 31370),
the two do not superpose correctly.

When importing the data into GRASS, I get perfect superposition. And when
I import the gps data into a GRASS 4326 location and the same data into a
31370 location, then reproject from one to the other, I also get perfect
superposition of the two versions of the gps data. However, when I export
to shapefiles from both locations and then load them in gvSIG indicating
their respective projections, I get a difference of about 100m.

Hamish Bowman suggested on the GRASS-users list that such a difference
hints at an issue with datum transformation.

I get the same kind of error using on-the-fly projection in QGIS.

Moritz