[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
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        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            
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Comment (by lutra):

 Hi,

 as you suggested I created two custom crs

 A) +proj=tmerc +lat_0=0 +lon_0=9 +k=0.9996 +x_0=1500000 +y_0=0 +ellps=intl
 +units=m +no_defs +datum=WGS84

 and

 B) +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
 +datum=WGS84


 which are basically the same of the two layers I attached to this ticket
 but with the "+datum" parameter.

 I then saved the *same* layer in two version with the above crs, to see if
 with OTFR enabled and the project defined in WGS84 (+proj=longlat
 +ellps=WGS84 +datum=WGS84 +no_defs) the two align*.

 When loading the layer defined with B) qgis strips or ignores

 "+towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68"

 and shows just

 "+proj=tmerc +lat_0=0 +lon_0=9 +k=0.9996 +x_0=1500000 +y_0=0 +ellps=WGS84
 +datum=WGS84 +units=m +no_defs"

 As said, trying to choose manually the crs doesn't change the situation.

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Ticket URL: <http://trac.osgeo.org/qgis/ticket/1875#comment:25>
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