[Gvsig_english] problems with on-the-fly projection

[Moritz Lennert]

On Sun, May 25, 2008 17:26, Marcus C. England wrote:
> Hi Moritz,
>
> GvSIG only reprojects vector data, not raster data. My understanding is
> that they hope to have this for rasters soon.

The two shapefiles I speak about below are vectors... And in the example
with the topo raster map, I reproject the GPS points/tracks (i.e. vectors)
to the projection of the topo map. And it works, but only more or less,
since the result is off by +/- 100m.

As I mentioned, QGIS has the same problem. See: 
http://trac.osgeo.org/qgis/ticket/1079.

Moritz

>
> -Marcus
>
> Moritz Lennert wrote:
>> 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
>>
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>
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