[QGIS-trac] Re: [Quantum GIS] #1079: on the fly projections do not work

[Quantum GIS]

#1079: on the fly projections do not work
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        Reporter:  pcav                                       |         Owner:  mhugent      
            Type:  defect                                     |        Status:  reopened     
        Priority:  critical: causes crash or data corruption  |     Milestone:  Version 1.0.0
       Component:  Projection Support                         |       Version:  HEAD         
      Resolution:                                             |      Keywords:  srs.db datum 
Platform_version:                                             |      Platform:  All          
        Must_fix:  Yes                                        |   Status_info:  1            
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Comment (by msieczka):

 Replying to [comment:16 neteler]:
 > I confirm that QGIS does not understand data in a GRASS location with
 towgs parameter:
 >
 > {{{
 > Warning: QgsCoordinateReferenceSystem::getRecord failed :  select * from
 tbl_srs where
 > parameters='+proj=tmerc +lat_0=0 +lon_0=9 +k=0.9996 +x_0=1500000 +y_0=0
 +ellps=intl
 > +towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68 +units=m +no_defs'
 > <snip>
 > }}}

 QGIS doesn't recognize this CRS, because epsg_tr.py (a GDAL utility, used
 in the QGIS CRS database creation script) will not create an exactly the
 same string for any EPSG code. I checked that with all EPSG codes against
 my GDAL 1.5.2 instalation. Markus, what EPSG code is this proj4 string
 supposed to represent?

 > Since GDAL considers this projection '''valid''', it must  be a QGIS
 problem. I take
 > liberty to reopen the ticket.

 True, the CRS definition is valid, in general, according to testepsg
 (another GDAL utility), yet it is not an exact representation of any EPSG
 code according to GDAL, as checked with epsg_tr.py.

 Looks like the bottom line of the problem is that QGIS uses an overly
 strict CRS matching. QGIS should support any CRS definition that GDAL
 considers valid, not only those which are exact equivalents of some EPSG
 codes.

 QGIS devs - can it? The testepsg from GDAL seems to provide the required
 functionality.

-- 
Ticket URL: <http://trac.osgeo.org/qgis/ticket/1079#comment:19>
Quantum GIS <http://qgis.org>
Quantum GIS is an Open Source GIS viewer/editor supporting OGR, PostGIS, and GRASS formats