[Proj] Coordinates transformation - Proj4, GDAL, OGR, PostGIS, MapServer

Antonin Orlik antonin.orlik.hgf at vsb.cz
Fri Dec 2 17:13:23 EST 2005

Dear developers,

I'm not sure who is responsible for the problem that I'm going to 
describe. This problem is very serious for me and for a lot of other 
people who are trying to use Open Source GIS software (especially in the 
Czech republic).

Library PROJ.4 has (next to the "*proj*" program) also program "*cs2cs*" 
("/The new *cs2cs* program performs a similar function to the *proj* 
program, but transforming from any one coordinate system to another. The 
new *pj_transform()* is used to access the extended coordinate system to 
coordinate system transformation with datum shifting/."). This program 
is a great thing, but unfortunately it looks like just a few GIS 
programs are using *cs2cs* instead of the *proj* program. For example, 
there is no problem with the coordinate transformation used in the 
PostGIS (which probably uses *cs2cs*). However,  the utilities of the 
*GDAL* and the *OGR* library, which are a base for a lot of other 
applications (MapServer, QGIS and so on), are probably using the *proj* 
program for coordinate transformations. This fact makes quite a big 
position shift after the coordinate transformation between coordinate 
systems based on diferent ellipsoids (*proj* program cannot make datum 
shifting). Finally, it is not possible to transform data correctly or to 
display more datasets based on different ellipsoids in a detailed view 
by the way of on-the-fly projection (the shift between elipsoids is 
often bigger than 100 meters).

Does somebody have any ideas? Is possible to make changes in the GDAL 
and OGR source codes and use the *cs2cs* instead of the *proj* program?

(probably to Frank Warmerdam)
In the Czech Republic we are using a strange coordinate system known as 
"krovak" (S-JTSK). This system has a strange axis orientation that is 
very hard to apply in the computer world, so nobody is using this axis 
orientation in GIS. Instead everybody is using switched axis ( X = -y, Y 
= -x ). If somebody would like to use proj.4 library, they have to use a 
patch for proj.4 library ( 
http://mpa.itc.it/radim/jtsk/PJ_krovak.c.patch ). For a lot of people it 
is very hard to apply this patch because they are just users who want to 
use an open source GIS software that uses proj.4 library. I can remember 
that this problem was discused by Radim Blazek and Frank Warmerdam but 
no successfull result were found... I think.

Is there any possibility to include this patch into an official version 
of proj.4 library? Or in the case that you want to keep this a 
"well-defined" krovak system, is possible to make a new definition of 
krovak with a different EPSG code (and keep the old one (esri:102065) in 
case there is an individual person who is using this definition)?

These two problems are major for a lot of people that I know and these 
are two of the main reasons why they are not going to use open source 
GIS software (and that is pity of course)...

Thank you for feedback.

Best regards,
Antonin Orlik

Ing. Antonin Orlik
Institute of Geoinformatics
VSB-Technical University of Ostrava
17.listopadu 15/2172
708 33 Ostrava-Poruba

E-mail: antonin.orlik.hgf at vsb.cz
Office: J 327
Tel: +420 59 732 3337
Mobile: +420 604 333 744
ICQ: 54928537

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