[OSRS-PROJ] datum shift Gauss Krueger
Markus Neteler
neteler at itc.it
Thu Jun 13 03:38:03 EDT 2002
Hi,
while not being very familiar with datum transformations, a suggestion
to below problem. The Peter Dana's web site shows a different
Potsdam_Rauenberg_DHDN datum:
http://www.colorado.Edu/geography/gcraft/notes/datum/dlist.html
A quick try:
cs2cs +proj=latlong +datum=WGS84 +to +init=epsg:31494 +towgs84=606,23,413
Some results with above datum:
Frans de Roos tried:
lat/long 11.60608768 48.25167084
new cs2cs: 4470850.92 5346045.81
expected: 4470860.075 5346044.934 (less error than he got, see below)
Harald Wehr tried:
lat/long 10.69079E 51.86134N
new cs2cs: 4409913.94 5748285.09
expected: 4409920 5748280 (less error than he got, see below)
Regards
Markus Neteler
On Thu, Jun 13, 2002 at 07:24:30AM +0200, 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
>
>
>
>
>
>
> Dear Frank,
>
> The Europeans like to do their rotations in an opposite direction from the
> rest of the world when doing 7-parameter Datum Shifts. Translation and
> Scale Factors remain the same. e.g., you will get weird and unexplainable
> results if you rotate in the wrong direction.
>
> A Helmert transform done with geocentric coordinates in three dimensions is
> called a Helmert Direct from Geodetic to Geocentric, and is called a
> Helmert Inverse from Geocentric to Geodetic.
>
> Molodensky-Badekas does a 3-d Helmert direct to geocentric coordinates,
> subtracts the geocentric coordinates of the classical Datum origin, then
> does the 7-parameter, then finally does the Helmert inverse back to the new
> Datum's geodetic coordinates.
>
> Bursa-Wolf does a 3-d Helmert direct to geocentric coordinates, does NOT
> subtract the geocentric coordinates of the classical Datum origin, then
> does the 3-parameter, or 4-parameter, or 7-parameter, then finally does the
> Helmert inverse back to the new Datum's geodetic coordinates.
>
> How do you tell which direction to rotate? It is impossible unless you
> have a test point. Since Harald does have a test point ...
>
> So now you know.
>
> Cliff
>
> Prof. Clifford J. Mugnier (cjmce at LSU.edu)
> Chief of Geodesy
> CENTER FOR GEOINFORMATICS
> Department of Civil Engineering
> LOUISIANA STATE UNIVERSITY
> Baton Rouge, LA 70803
> Voice and Facsimile: (225) 578-8536
> Pager: 1-(888) 365-5180
> ================================
> http://www.ASPRS.org/resources.html
> http://www.ce.LSU.edu/~mugnier/
> ================================
>
>
> Harald Wehr wrote:
> > Hi Frank,
> >
> > first i apologize, that i contact you directly.
> >
> > In the PROJ.4-mailing-list no one answered to my problem. Attached you
> > find my mail from february 26th that I send to the list.
> ...
>
> > I want to convert some data from latlong/wgs84 to tmerc/bessel with
> > datum shift from wgs84 to potsdam-datum here in germany. How do i have
> > to use the function? Are helmert-7-parameter as well as
> > molodenski-3-parameter implemented? I tried the following:
>
> Harald,
>
> I didn't answer because I am always getting confused about the terminology
> for some of the different transforms. There is a three and seven
> parameter transform implemented; however, I am not certain that the
> interpretation of the parameters (sign, handedness, etc) is exactly what
> is defined for helmert and molodenski. I think it is though.
>
> >
> > --------
> > cs2cs -v +proj=latlong +to +proj=tmerc +ellps=bessel +lat_0=0 +lon_0=12
> > +x_0=4500000 +towgs84=-586,-87,-409 <<EOF
> > 10.69079E 51.86134N
> > EOF
> > --------
> >
> > As result i get the following:
> >
> > ---------
> > # ---- From Coordinate System ----
> > #Lat/long (Geodetic)
> > #
> > # +proj=latlong +ellps=WGS84
> > # ---- To Coordinate System ----
> > #Transverse Mercator
> > # Cyl, Sph&Ell
> > # +proj=tmerc +ellps=bessel +lat_0=0 +lon_0=12 +x_0=4500000
> > # +towgs84=-586,-87,-409
> > #--- following specified but NOT used
> > # +ellps=WGS84
> > 4409820.23 5748070.07 698.769
> >
> > ---------
> >
> > The result is not good enough. I expect something like that:
> > 4409920 5748280.
> >
> > Whats wrong here? I got the "towgs"-parameters from a another
> > helmert-calculation i found in the internet which work in another
> > program i have here and show the results i expected.
>
> First, no actual datum shift is being applied in this case because PROJ
> doesn't equate +ellps=WGS84 with the WGS84 datum automatically. I realized
> this when I did the conversion without the +towgs84 parameter and got the
> same results. Please use +datum=WGS84 to force treatment of the lat/long
> coordinates as being the WGS84 datum.
>
> Howwever, this doesn't seem to get us any closer to your expected values.
>
> warmerda at gdal[355]% cs2cs +proj=latlong +datum=WGS84 +to +proj=tmerc
> +ellps=bessel
> +lat_0=0 +lon_0=12 +x_0=4500000 +towgs84=-586,-87,-409 < test.dat
> 4409793.19 5747857.54 1386.040
>
> I tried reversing the sign of the offset, as this is a frequent
> incompatibility,
> and get:
>
> warmerda at gdal[356]% cs2cs +proj=latlong +datum=WGS84 +to +proj=tmerc
> +ellps=bessel
> +lat_0=0 +lon_0=12 +x_0=4500000 +towgs84=586,87,409 < test.dat
> 4409847.28 5748282.64 11.504
>
> This is close to what you expect in the northing (2m), but no so close in
> the
> easting - still off by 70m or so. I am no sure what else to say.
>
> Best regards,
>
>
>
>
>
>
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