[GRASS-user] gps import: definition of WGS84
hamish_b at yahoo.com
Sun May 25 09:16:09 EDT 2008
> Thanks to everyone for their answers. I've tried all the
> different suggestions and the answer seems to be clear:
> on-the-fly projection does not work properly in QGIS and gvSIG...
> Whatever I do in GRASS, I always get correct placement of the GPS data.
This seems to be QGIS bug # 1079
(usual suspects reporting in :)
> Using on-the-fly projection in the other programs, I get a
> difference of about 100m, so I guess it's a datum issue as
> Hamish suggests.
It would seem so. I can reproduce it here (see bug report). In my case looking in the layer's "P"roperies projection tab I see the the +datum= and/or +towgs84= terms are missing* versus what is found in the EPSG file.
[*] file: /usr/share/qgis/resources/srs.db (SQLite DB)
Root cause seems to be that QGIS lacks a "pick appropriate datum transform parameters to use" GUI in the case when there are multiple possibilities, and so it doesn't try any datum transform at all:
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