[Proj] datum conversion, estimating parameters

Eric Miller EMiller at dfg.ca.gov
Fri Mar 25 14:28:22 EST 2005

+ellps=bessel and +datum=WGS84 do not go together.  The WGS84 datum uses
the WGS84 ellipsoid.  I'd think specifying the datum in cs2cs would
override your erroneous ellipsoid specification, but I guess it

Eric G. Miller
GIS Analyst
Wildlife and Habitat Data Analysis Branch
Department of Fish and Game

>>> robert-j at gmx.de 03/25/05 11:01 AM >>>


I "proj'ed" much the last days and for locating points on a
georeferenced TK25 I use GPSman. And I don't know, if I did something
wrong again, or if this is an error in GPSman or proj:

DMS/WGS84: 12d10'27.4"E  51d41'38.3"N 
UTM/WGS84: 33U  304711 5730783  (says GPSman)
GKK/WGS84:   4 4512051 5729309  (says GPSman)

> proj +proj=utm +zone=33
12d10'27.4"E  51d41'38.3"N
304710.92       5730782.08
> proj +proj=tmerc +lat_0=0 +lon_0=12 +k=1.000000 +x_0=4500000 +y_0=0
12d10'27.4"E  51d41'38.3"N
4512049.02      5728718.94
> cs2cs +proj=latlong +datum=WGS84 +to +proj=tmerc +lat_0=0 +lon_0=12
+k=1.000000 +x_0=4500000 +y_0=0 +ellps=bessel +datum=WGS84
12d10'27.4"E  51d41'38.3"N
4512049.17      5728654.21 698.95

I cannot explain the difference in the northing in the last two
conversions (proj does no datum shift and cs2cs shouldn't, because I
said "+datum=WGS84"). The question is: which are the correct GKK/WGS84
coordinates? The ones from GPSman or the ones from proj or from cs2cs?

Thank you again, Robert

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