[Proj] Long/Lat -> Gauss-Krueger, wrong coordinates?!
O.Rahn at fh-osnabrueck.de
Wed Nov 24 10:05:30 EST 2004
thank you very much for your suggestion!
I didn't know anything about those parameters before, so I googled
around a little bit and found some parameters for "Rauenberg" (a city
near Potsdam - see: www.ottmarlabonde.de/L1/datum.html). On that page is
also an applet that can transform single pairs of coordinates.
My results didn't get better when I inserted the "towgs84" parameter
("+proj=tmerc +ellps=bessel +lat_0=0 +lon_0=9 +k=1.000000 +x_0=3500000
+units=m no_defs"). So, I used the applet on the page mentioned above to
see if the page-guy would get the same results. He didn't. His results
(same 7 parameters) are what I would expect.
Digging a little bit deeper into the contents of his page I found a spot
where he writes about the accuracy of his calulations depending on the 7
parameters: In the worst case his coordinates were about 1.5 meters off
- mine are about 160 meters off.
I think there has to be something else that is seriously wrong with my
parameters (?) or ... something.
Maybe you have some other idea?
>I suppose the reason are the 7 datum transformation parameters defining the spatial location of the Bessel to WGS-84 ellipsoid (towgs84 parameter). I suppose ther are 7 parameters with no shifts and rotations and scale 1.0 used by default in proj. Define the proper parameter and it will work. There are differnet parameters sets used in Germany. Try to find out which one are used for your reference coordinates.
>For example this is one set for a local area in South Germany (just to get an idea of the size of the parameters): +towgs84=591.28,81.35,396.39,1.477,-0.0736,-1.458,9.82
>O.Rahn at fh-osnabrueck.de schrieb am 24.11.04 11:14:18:
>>I'm sure I'm doing something obvious wrong, but I just don't see it...
>>I have got a problem projecting some coordinates form a
>>longitude/lattitude (WGS84) coordinate system to Gauss-Krueger Zone 3
>>projection using proj:
>>The resulting (Gauss-Krueger) coordinates are not what they should be
>>according to my reference dataset. They seem to be about 150 and 70
>>meters off in North and East direction.
>>The parameters I supply proj with are:
>>"+proj=tmerc +lat_0=0 +lon_0=9 +k=1.000000 +x_0=3500000 +y_0=0
>>+ellps=bessel +units=m no_defs" (to translate the WGS84 coordinates to
>>GK Zone 3)
>>(As far as I know I don't have to reproject the WGS84 coordinates to
>>something else, because Proj uses WGS84 (= no projection) as "base
>>format" - right?)
>>I got those parameters from an EPSG-list (EPSG 31463 - "DHDN / 3-degree
>>Gauss zone 3"), so they appear to be right to me...
>>If I use this projection parameters, the coordinates of e.g. a point
>>change as follows:
>>original coordinates: 8.05864684 (east), 52.322994 (north)
>>resulting GK coords: 3435824.638, 5799103.492
>>but they should be something like: 3435898, 5799265
>>What am I doing wrong??
>>Any other suggestions or hints?
>>Thank you in advance!
>>Proj mailing list
>>Proj at xserve.flids.com
>Mit WEB.DE FreePhone mit hoechster Qualitaet ab 0 Ct./Min.
>weltweit telefonieren! http://freephone.web.de/?mc=021201
>Proj mailing list
>Proj at xserve.flids.com
Tel.: 0541 969 3617
mail.: O.Rahn at FH-Osnabrueck.de
More information about the Proj