[Proj] datum conversion, estimating parameters

Clifford J Mugnier cjmce at lsu.edu
Fri Mar 25 15:20:29 EST 2005


Actually that's not always the case.  There are some really screwy
contrivances that are coming out of far-off places with regard to "new"
datum definitions.  Wrong, of course, but still "official" with respect to
locals.  For instance, there is such a weird combination of WGS84 positions
combined with the Everest 1830 ellipsoid for the "new" datum of Sri Lanka.
The "new" system in the Philippines is a close second.  There's others, too

Not so in Germany, though.  I think they have the highest population
density of Geodesists per square meter in the world.


Happy Easter!  Watch 'dem eggs ...

Clifford J. Mugnier
Chief of Geodesy and
Associate Director,
Department of Civil Engineering
CEBA 3223A
Baton Rouge, LA  70803
Voice and Facsimile:  (225) 578-8536 [Academic]
Voice and Facsimile:  (225) 578-4474 [Research]

+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

"I have been a happy man ever since January 1, 1990, when I no longer
had an
email address. I'd used email since about 1975, and it seems to me that
years of email is plenty for one lifetime."
--- Donald E. Knuth

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