[OSRS-PROJ] datum shift Gauss Krueger

Markus Neteler neteler at itc.it
Thu Jun 13 00:38:03 PDT 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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