[OSRS-PROJ] datum shift Gauss Krueger

[Frank Warmerdam]

Frans de Roos (EPL) wrote:
> Hello All
> 
> I got the same problem as Harald Wehr when tranforming from wgs84 to Gauss-Krueger (zone 4) . My transformation will also be about 55 meters wrong.
> 
> I use cs2cs as follow
> cs2cs +proj=latlong +datum=WGS84 +to +proj=tmerc +ellps=bessel
> +lat_0=0 +lon_0=12 +x_0=4500000 +towgs84=583,68,399
> 
> What I know from some other program I should use 
> 
> Gauss Krueger 4, Bessel, Potsdam_IST_V2_0 
> 583.00     - Translation dx in meter to WGS84
> 68.0       - Translation dy in meter to WGS84
> 399.50     - Translation dz in meter to WGS84
> 0          - Rotation ro (omega) in Radiant to WGS84
> 0          - Rotation rf (phi) in radiant to WGS84
> 13.6e-06   - Rotation rk (Kappa) in Radiant to WGS84
> 11.3e-06   - Mapscale factor in ppm (parts per million) to WGS84
> 
> And tranformation should calculate
> 
> ID  lon (WGS84)  lat (WGS84)    X (GK4)      Y (GK4)
> 1   11.60608768  48.25167084    4470860.075  5346044.934
> 2   10.96510029  50.25949478    4426313.445  5569780.810
> 3   7.46         51.57          4185407.951  5724830.919
> 
> When I use cs2cs I get the X-value to be about 55 meters wrong! The Y-value will just differ 0 - 3 meter.
> I think that I should in some way add the rotation kappa in the calculation! Does anyone know how how I should do this?
> 
> If I change the dy value from 68 to 18 I got some better values. Now the X and Y values will differ about 8 meters but I don't think I should do this.

Frans,

I am not sure how good the datum shift parameters you received are.  However,
just dropping the rototational and scaling parameters can be unwise.  Also,
the expression (units) of the rotational and scaling parameters are different
than that used for the 7 parameter shift in EPSG transformation 9606.  While
there must be a formula to translate, I don't know it.

I have written up some description of my understanding of the PROJ.4 datum
shifting in:

  http://www.remotesensing.org/proj/gen_parms.html

Best regards,
-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent


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