# DHDN / Gauss Krueger to WGS84

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## DHDN / Gauss Krueger to WGS84

 Hi, looks like this question has been posted in the past, but blimey, I could not extract a simple answer that I do understand. Thus  I would like to rephrase the question in the hope to get an easy to use answer for someone not deep in geo math at all :) I do have a coordinate in easting/northing [m] from a raster map  using Gauss Krüger projection and Potsdam datum. Now I would like to get the lon/lat coordinate on a WGS84 ellipsoid. And vice versa. I would like to use the proj4 C API not the command line. Can any kind soul take me by the hand and point me to some tutorial or give me a quick guided tour? Thanks, Oliver _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

 > I do have a coordinate in easting/northing [m] from a raster map  using > Gauss Krüger projection and Potsdam datum. Now I would like to get the > lon/lat coordinate on a WGS84 ellipsoid. And vice versa. I would like to > use the proj4 C API not the command line. > >   Ok, further investigations condensed into something like: pjgaukru = pj_init_plus("+init=epsg:31467"); pjwgs84 = pj_init_plus("+init=epsg:4326"); // easting / northing to lon / lat pt = pj_inv(pt,pjgaukru) //??? double z = 0; pj_datum_transform(pjgaukru, pjwgs84, 1, 0, &pt.u, &pt.v, &z); However the result is still several minutes away from the expected coordinate. What do I miss? Oliver _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

 Oliver Eichler wrote: >> I do have a coordinate in easting/northing [m] from a raster map  using >> Gauss Krüger projection and Potsdam datum. Now I would like to get the >> lon/lat coordinate on a WGS84 ellipsoid. And vice versa. I would like to >> use the proj4 C API not the command line. >> >>   > > Ok, further investigations condensed into something like: > > pjgaukru = pj_init_plus("+init=epsg:31467"); > pjwgs84 = pj_init_plus("+init=epsg:4326"); > > // easting / northing to lon / lat > pt = pj_inv(pt,pjgaukru) > > //??? > double z = 0; > > pj_datum_transform(pjgaukru, pjwgs84, 1, 0, &pt.u, &pt.v, &z); > > However the result is still several minutes away from the expected > coordinate. What do I miss? Oliver, How about: pjgaukru = pj_init_plus("+init=epsg:31467"); pjwgs84 = pj_init_plus("+init=epsg:4326"); //??? double z = 0; pj_datum_transform(pjgaukru, pjwgs84, 1, 0, &pt.u, &pt.v, &z); Don't forget that the output is pt.u with the longitude in radians, and pt.v with the latitude in radians.  The call you make to pj_inv() is duplicating work that is done by pj_transform() (corrupting really). I would add that epsg:31467 expands as: +proj=tmerc +lat_0=0 +lon_0=9 +k=1.000000 +x_0=3500000 +y_0=0 +ellps=bessel +datum=potsdam +units=m +no_defs Note that this definition is using +datum=potsdam which expands to:    +ellps=bessel +towgs84=606.0,23.0,413.0 This may or may not be the best datum shift parameters for your area of work.  You may need to research a better local shift. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up   | Frank Warmerdam, [hidden email] light and sound - activate the windows | http://pobox.com/~warmerdamand watch the world go round - Rush    | President OSGeo, http://osgeo.org_______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

 Hi Frank > pjgaukru = pj_init_plus("+init=epsg:31467"); > pjwgs84 = pj_init_plus("+init=epsg:4326"); > > //??? > double z = 0; > What is the z parameter for? Height? > > I would add that epsg:31467 expands as: > > +proj=tmerc +lat_0=0 +lon_0=9 +k=1.000000 +x_0=3500000 +y_0=0 > +ellps=bessel +datum=potsdam +units=m +no_defs > > Note that this definition is using +datum=potsdam which expands to: > >   +ellps=bessel +towgs84=606.0,23.0,413.0 > That should be ok. These are maps from "Bayerisches Landesvermessungsamt". Hope they know what they are doing. > This may or may not be the best datum shift parameters for your area of > work.  You may need to research a better local shift. > Does that mean that the shift parameters depend on the location within the map? Or that the whole map might have some kind of bad offset produced by a bad projection? And how would I get better shift parameters? Is there a tutorial somewhere? Thanks, Oliver _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

 Oliver Eichler wrote: >> This may or may not be the best datum shift parameters for your area of >> work.  You may need to research a better local shift. >> > Does that mean that the shift parameters depend on the location within > the map? Or that the whole map might have some kind of bad offset > produced by a bad projection? > > And how would I get better shift parameters? Is there a tutorial somewhere? Oliver, The 3/7 parameter +towgs84 parameters are just used for an approximate transformation between datums. Sometimes, especially for old datums, the differences are quite irregular over the area of the datum and are not well represented by a simple transformation. So, you will often see datums having various towgs84 parameters, some which might be a decent general transformation over a large area and others which might be a more accurate transformation in a fairly local area of the datum. Ugly, isn't it? No, there is no obvious way to get better parameters other than researching various source (ie. national mapping agencies, other publications, ask other users in your region). Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up   | Frank Warmerdam, [hidden email] light and sound - activate the windows | http://pobox.com/~warmerdamand watch the world go round - Rush    | President OSGeo, http://osgeo.org_______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

 > > Ugly, isn't it? > > No, there is no obvious way to get better parameters other than > researching > various source (ie. national mapping agencies, other publications, ask > other > users in your region). > Hi Frank, I feared you will say that. Well as the original data and software is able to geo-reference the map correctly I guess I have to look for the 3 or 7 values in the original data. At least I know now what to look for :) On last question: the z parameter for pj_transform() is the height isn't it? Oliver _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## AW: DHDN / Gauss Krueger to WGS84

 In reply to this post by Oliver Eichler-2 Oliver, > > Oliver Eichler wrote: > >> This may or may not be the best datum shift parameters for > your area of > >> work.  You may need to research a better local shift. > >> > > Does that mean that the shift parameters depend on the > location within > > the map? Or that the whole map might have some kind of bad offset > > produced by a bad projection? > > > > And how would I get better shift parameters? Is there a > tutorial somewhere? > > Oliver, > > The 3/7 parameter +towgs84 parameters are just used for an approximate > transformation between datums. Sometimes, especially for old > datums, the > differences are quite irregular over the area of the datum > and are not well > represented by a simple transformation. > > So, you will often see datums having various towgs84 > parameters, some which > might be a decent general transformation over a large area > and others which > might be a more accurate transformation in a fairly local area of the > datum. > > Ugly, isn't it? > > No, there is no obvious way to get better parameters other > than researching > various source (ie. national mapping agencies, other > publications, ask other > users in your region). please take a look at http://crs.bkg.bund.de/crseu/crs/descrtrans/BeTA/de_dhdn2etrs_beta.phpThere you will find information about a "standard" solution for your problem. The documentation gives a brief example for using PROJ.4. (I think, the german language isn't a problem for you :-)). If you have any problems, please let me know. Best wishes Uwe --------------------------------------------------------- ... Uwe Schmitz  Landesvermessungsamt Nordrhein-Westfalen ... Muffendorfer Str. 19 - 21              D - 53177 Bonn ... E-mail:       [hidden email] ... Internet:     http://www.lverma.nrw.de_______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

 In reply to this post by Oliver Eichler-2 Oliver Eichler wrote: > On last question: the z parameter for pj_transform() is the height isn't > it? Oliver, Yes, sorry for not answering that aspect the first time around. Some transformation (such as datum shifts and changes of ellipsoid) can also alter the elevation about the ellipsoid so we provide a z to transform even if we ignore the results. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up   | Frank Warmerdam, [hidden email] light and sound - activate the windows | http://pobox.com/~warmerdamand watch the world go round - Rush    | President OSGeo, http://osgeo.org_______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: AW: DHDN / Gauss Krueger to WGS84

 In reply to this post by Uwe Schmitz-2 [hidden email] wrote: > please take a look at > http://crs.bkg.bund.de/crseu/crs/descrtrans/BeTA/de_dhdn2etrs_beta.php> > There you will find information about a "standard" solution > for your problem. The documentation gives a brief example > for using PROJ.4. (I think, the german language isn't a problem > for you :-)). > > If you have any problems, please let me know. > >   Hi Uwe Ok, had a look at it. Maybe it's a dump question (I am really not professional in this area) but as my target datum is WGS84 shouldn't I use different shift factors than for ETRS89? Or is the shift from ETRS89 to WGS84 independent from the actual location? Google gives me the impression that it is. Oliver _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: AW: DHDN / Gauss Krueger to WGS84

 Hi Oliver,   No question is ever dumb. If no one ever asks, no one can ever learn.   A technical definition from Wikipedia states:   "The European Terrestrial Reference System 1989, usually referred to as ETRS89, is a three-dimensional geodetic frame of reference - a mapping coordinate system used as the standard high accuracy system for GPS in Europe.   It coincided with the World Geodetic System 1984 in 1989, hence the name, and is based on the same GRS80 ellipsoid. Unlike WGS84 or ITRS it is centred on Europe and diverges from them with the movements of the tectonic plates associated with this landmass."   Please see: http://en.wikipedia.org/wiki/ETRS89 for ETRS89   These are some pretty good description of some systems used in Geodesy.   Cheers, Dean     ----- Original Message -----From: Oliver Eichler <[hidden email]>Date: Friday, September 21, 2007 8:59 amSubject: Re: AW: [Proj] DHDN / Gauss Krueger to WGS84To: "PROJ.4 and general Projections Discussions" <[hidden email]>> [hidden email] wrote:> > please take a look at > > > http://crs.bkg.bund.de/crseu/crs/descrtrans/BeTA/de_dhdn2etrs_beta.php>> > There you will find information about a "standard" solution > > for your problem. The documentation gives a brief example> > for using PROJ.4. (I think, the german language isn't a problem> > for you :-)).> >> > If you have any problems, please let me know.> >> >   > Hi Uwe> > Ok, had a look at it. Maybe it's a dump question (I am really not> professional in this area) but as my target datum is WGS84 > shouldn't I> use different shift factors than for ETRS89?> > Or is the shift from ETRS89 to WGS84 independent from the actual> location? Google gives me the impression that it is.> > Oliver> _______________________________________________> Proj mailing list> [hidden email]> http://lists.maptools.org/mailman/listinfo/proj> Dean C. Mikkelsen, B.Sc., P.Eng. Terra ETL Ltd. Mobile/Cellphone: +1 250 361 6672 E-mail: [hidden email] _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: AW: DHDN / Gauss Krueger to WGS84

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## DHDN / Gauss Krueger to WGS84

 In reply to this post by Oliver Eichler-2 Dean, very good explanation, thank you! Regards, Uwe _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

 Hi Uwe and Dean, it seems to work. A reference point of: x = 4459750 m  y = 5448182 m is converted to E11.446588 N49.169494 The GeoGrid Viewer (Uwe should know) tells me: E11.44662  N49.16951 That is approx. 1 or 2 meters apart. I can't tell if that is a normal error because of the different calculation code. But I guess I have to be happy with it :) . BTW can anyone tell me why on earth the Europeans define a datum that is identical to WGS84 in 1989 but will have an increasing error over the years? Is that politics or just to keep things, located in Europe, from 'moving' (in respect to WGS84)? Thank you all for your answers. Oliver _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: AW: DHDN / Gauss Krueger to WGS84

 In reply to this post by Oliver Eichler-2 Hello all! We have solved this problem with moving plates by adding a simple date with the coordinates of WGS84. That way you can always go back to the original position of that particular date in WGS84 (or any). The WGS84 datum (with date)  will stay accurate for ever, since it is always possible to trace back where the plates were at that specific date. latitude, longitude, (WGS84), date That's it. At the moment we don't need this feature, but it is there to be sure that the positions recorded will always stay accurate. Regards Janne. --------------------------------- > I forgot to add the following: >   > The parameters for a datum shift (dx, dy, dz, rx, ry, rz, etc.) between ETRS89 and WGS84 are not constant, due to the movement of the Eurasian geophysical plate with respect to WGS84. The differences between both datums can grow by several centimetres a year. Currently they are a couple of decimetres in difference. For many applications, these differences are not relevant. Coordinates or positions in WGS84 have usually been obtained by GPS and this results in an accuracy at the level of several metres. However, satellite positioning techniques continuously improve in accuracy, also without using differential stations. So the differences between the datum's will grow. Note that many nations are using WGS84 to define boundaries nowadays - so WGS84 is relevant. >   > In your case and for your application, I do believe you will be fine using ETRS89. >   > Cheers, > Dean -- _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

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## Re: DHDN / Gauss Krueger to WGS84

 Bad form to reply to my own post, but... > > I would add that epsg:31467 expands as: > > > > +proj=tmerc +lat_0=0 +lon_0=9 +k=1.000000 +x_0=3500000 +y_0=0 +ellps=bessel > > +datum=potsdam +units=m +no_defs > > it seems to work. A reference point of: > > > > x = 4459750 m  y = 5448182 m > > > > is converted to > > > > E11.446588 N49.169494 > > > If I use pj_transform(), I get: >   >   21.982946, 48.433278 I see that cs2cs gives the same incorrect result I get, and not the expected result: cs2cs +init=epsg:31467 +to +init=epsg:4326 4459750 5448182 21d58'58.607"E  48d25'59.803"N -15.126 Yours sincerely, Roger Oberholtzer OPQ Systems / Ramböll RST Office: Int +46 10-615 60 20 Mobile: Int +46 70-815 1696 [hidden email] ________________________________________ Ramböll Sverige AB Krukmakargatan 21 P.O. Box 17009 SE-104 62 Stockholm, Sweden www.rambollrst.se _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

 On 30/03/2012 12:23, Roger Oberholtzer wrote: > I see that cs2cs gives the same incorrect result I get, and not the > expected result: > > cs2cs +init=epsg:31467 +to +init=epsg:4326 > 4459750 5448182 > 21d58'58.607"E  48d25'59.803"N -15.126 > > If your x-value starts with a 4, shouldn't it then be GK zone 4 = epsg:31468 ? \$ echo "4459750 5448182" | cs2cs +init=epsg:31468 +to +init=epsg:4326 11d26'47.703"E  49d10'10.159"N 50.082 Hermann _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

 In reply to this post by Roger Oberholtzer Hello Roger, Actually, I do believe that E 21.982946, N 48.433278 is the correct result, or at least more correct than E 11.446588, N 49.169494. Here is how I convinced myself: Since x = 4459750 m and the False Easting is 3500000, the point is 4459750 - 3500000 = 959750 m east of the central meridian which is 9° E. At the equator, there are about 111120 meters per degree, so if we were at the equator we would be 959750 / 111120 = 8.64° east of the central meridian.  But at the approximate latitude 49° N, the meridians are closer together by a factor cos(49°), so we are really about 8.64°/cos(49°) = 13.17° degrees east of the central meridian, which is 22.17° east of Greenwich. This is of course just a rough calculation, ignoring the changing local scale of the projection etc, but I think it shows that the longitude should be nearer 22°E than 11°E. I don't know what's wrong with the original test example. (For a while, I was thinking it had to do with the axis order,  since in EPSG:31467, x should be northing and y easting.  But 4459750 m cannot be a northing here, since it would  be too far south, somewhere in south Italy.  So I suppose your test example does use the mathematical  convention after all, with x as easting and y as northing.) Best regards, Mikael Rittri Carmenta Sweden http://www.carmenta.com-----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Roger Oberholtzer Sent: Friday, March 30, 2012 12:23 PM To: PROJ.4 and general Projections Discussions Subject: Re: [Proj] DHDN / Gauss Krueger to WGS84 Bad form to reply to my own post, but... > > I would add that epsg:31467 expands as: > > > > +proj=tmerc +lat_0=0 +lon_0=9 +k=1.000000 +x_0=3500000 +y_0=0 +ellps=bessel > > +datum=potsdam +units=m +no_defs > > it seems to work. A reference point of: > > > > x = 4459750 m  y = 5448182 m > > > > is converted to > > > > E11.446588 N49.169494 > > > If I use pj_transform(), I get: >   >   21.982946, 48.433278 I see that cs2cs gives the same incorrect result I get, and not the expected result: cs2cs +init=epsg:31467 +to +init=epsg:4326 4459750 5448182 21d58'58.607"E  48d25'59.803"N -15.126 Yours sincerely, Roger Oberholtzer OPQ Systems / Ramböll RST Office: Int +46 10-615 60 20 Mobile: Int +46 70-815 1696 [hidden email] ________________________________________ Ramböll Sverige AB Krukmakargatan 21 P.O. Box 17009 SE-104 62 Stockholm, Sweden www.rambollrst.se _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj_______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

 On 30/03/2012 13:38, Mikael Rittri wrote: > Hello Roger, > > Actually, I do believe that E 21.982946, N 48.433278 is the correct > result, or at least more correct than E 11.446588, N 49.169494. > > Here is how I convinced myself... Here is how I convinced myself that the opposite is true: - DHDN = Deutsches_Hauptdreiecksnetz, a Datum used in Germany, i.e. not used at E 21.982946 - in a coordinate system based on 3-degree zones, it doesn't make much sense to have x-values which are 959750 m east of any central meridian - at school, I learned: if the leading digit of the x-value is 4, than you are in 3-degree Gauss-Kruger zone 4 (nowadays also known as epsg:31468) - GK3 zone 4 has a central meridian of 12 degrees East and a false easting of 4500000m, see also [1] Given the above, you end up with: echo "4459750 5448182" | cs2cs -f "%.6f" +init=epsg:31468 +to +init=epsg:4326 11.446584       49.169489 50.081973 (i.e. some 100+ km north of Munich) Hermann [1] http://upload.wikimedia.org/wikipedia/de/1/12/Gau%C3%9F-Kr%C3%BCger-Raster_Deutschland.png_______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: DHDN / Gauss Krueger to WGS84

 Hermann, you are right, of course. In the original thread, DHDN zone 3 was mentioned, but the discussion was mainly about the datum shift. Later in the thread, the test point was given, but without a zone number. (I suppose all German GIS people know that the leading digit of the Easting is the zone number.) Thanks, Mikael Rittri Carmenta Sweden http://www.carmenta.com-----Original Message----- From: Hermann Peifer [mailto:[hidden email]] Sent: Friday, March 30, 2012 2:10 PM To: PROJ.4 and general Projections Discussions Cc: Mikael Rittri Subject: Re: DHDN / Gauss Krueger to WGS84 On 30/03/2012 13:38, Mikael Rittri wrote: > Hello Roger, > > Actually, I do believe that E 21.982946, N 48.433278 is the correct > result, or at least more correct than E 11.446588, N 49.169494. > > Here is how I convinced myself... Here is how I convinced myself that the opposite is true: - DHDN = Deutsches_Hauptdreiecksnetz, a Datum used in Germany, i.e. not used at E 21.982946 - in a coordinate system based on 3-degree zones, it doesn't make much sense to have x-values which are 959750 m east of any central meridian - at school, I learned: if the leading digit of the x-value is 4, than you are in 3-degree Gauss-Kruger zone 4 (nowadays also known as epsg:31468) - GK3 zone 4 has a central meridian of 12 degrees East and a false easting of 4500000m, see also [1] Given the above, you end up with: echo "4459750 5448182" | cs2cs -f "%.6f" +init=epsg:31468 +to +init=epsg:4326 11.446584       49.169489 50.081973 (i.e. some 100+ km north of Munich) Hermann [1] http://upload.wikimedia.org/wikipedia/de/1/12/Gau%C3%9F-Kr%C3%BCger-Raster_Deutschland.png_______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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