[Proj] *SOLVED*: Creating a nadgrid shift file with GDAL
j.l.h.hartmann at uva.nl
Mon Jan 21 11:41:30 EST 2013
All excellent remarks, but I'm not sure of nr 1
On 01/21/2013 04:42 PM, Andre Joost wrote:
> 1) transfer the original coordinates to latlon, without a wgs84 shift
> Why that? If you want to use the self-defined CRS in Qgis, it should
> better be in "real" WGS84 coordinates, that is with the +towgs84
> parameters. After all, its the position of the bessel ellipsoid relative
> to the WGS84 ellipsoid we now all reference to. Your old CRS may have
> the same position, though.
The shift is from the original ellipsoid to wgs84, so I think the
distances should be computed from different ellipses. I'l try it out
next few days.
If you want, I could send you the proj parameters for the Tranchot-map,
together with the 48 original triangulation points, both in the original
coordinate system and Gauss-Krüger II, as computed by Rodulf Schmidt in
1973. You can see a rough georeference (without shifts) at
http://mapserver.sara.nl/zl/, and the way it did it on:
http://mapserver/conferences/2007/berlin_fossgis/. I'm certainly going
to compute a shift file for it, when I get time for it, but if you want
to try your hand on it, you are very welcome.
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