[QGIS-trac] Re: [Quantum GIS] #1875: A few problems with crs definitions with TOWGS parameters

[Quantum GIS]

#1875: A few problems with crs definitions with TOWGS parameters
--------------------------------------------------------------+-------------
        Reporter:  lutra                                      |         Owner:  homann       
            Type:  bug                                        |        Status:  closed       
        Priority:  critical: causes crash or data corruption  |     Milestone:  Version 1.2.0
       Component:  Projection Support                         |       Version:  HEAD         
      Resolution:  fixed                                      |      Keywords:               
Platform_version:                                             |      Platform:  All          
        Must_fix:  No                                         |   Status_info:  0            
--------------------------------------------------------------+-------------
Changes (by homann):

  * status:  reopened => closed
  * resolution:  => fixed

Comment:

 Since version 4.6.0 of the PROJ.4 library we use for transformation, the
 +towgs84 is not handled unless both CRS:es have a +datum specified.

 Using proj 4.4.9, there is a notable shift in the layers when using
 projection.

 With 4.6.0, a workaround is to manually define a custom CRS that have a
 datum specifie, e.g. adding a "+datum=WGS84" string. In this case, the
 layer fauglia.shp can be set to a custom projection, with +datum=WGS84 and
 a notable shift occur.

 NOTE: I haven't verified that the shifts of the layers are correct, only
 that they occur.

-- 
Ticket URL: <https://trac.osgeo.org/qgis/ticket/1875#comment:22>
Quantum GIS <http://qgis.org>
Quantum GIS is an Open Source GIS viewer/editor supporting OGR, PostGIS, and GRASS formats