[QGIS-trac] [Quantum GIS] #3645: synchronize QGIS' SRS definitions with GDAL's 1.8.0 SRS database

[Quantum GIS]

#3645: synchronize QGIS' SRS definitions with GDAL's 1.8.0 SRS database
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   Reporter:  nirvn                                      |              Owner:  nobody       
       Type:  bug                                        |             Status:  new          
   Priority:  critical: causes crash or data corruption  |          Milestone:  Version 1.7.0
  Component:  Projection Support                         |            Version:  Trunk        
   Keywords:                                             |   Platform_version:               
   Platform:  All                                        |           Must_fix:  Yes          
Status_info:  0                                          |  
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 Some QGIS´ SRS definitions are missing towgs84 values, including UTM
 Indian 1960 48N, resulting in misalignment of mixed-datum layers with
 projects with on the on the fly reprojection set.

 Folks from the #gdal IRC channel said QGIS should update/synchronize it's
 SRS definition database with GDAL's 1.8.0 SRS database.

 I can confirm that creating a custom SRS using GDAL's version of the UTM
 Indian 1960 48N definition (same as QGIS except QGIS misses the +towgs84
 value) fixed all of my reprojection problems.

 (see a bunch of screenshots with misaligned vectors from this now invalid
 ticket: http://trac.osgeo.org/qgis/ticket/3632)

 Pasting some useful bits from a discussion in #gdal:
 <nIRV> EvenR, what would explain a difference in reprojection between qgis
 and gdal?
 <EvenR> it might depend on the GDAL version you have and the definition
 that QGIS uses for EPSG:3148. GDAL 1.8.0 has a
 TOWGS84[198,881,317,0,0,0,0] for EPSG:3148.
 <EvenR> you have to check what SRS definition qgis uses for EPSG:3148. I
 suspect it has not the TOWGS84 shift
 <nIRV> +proj=utm +zone=48 +a=6377276.345 +b=6356075.41314024 +units=m
 +no_defs
 <nIRV> indeed, there's no towgs84 in the qgis definition
 <EvenR> it could be appropriate that it synchronizes its SRS definitions
 (for that one, and also for others) with GDAL 1.8.0 SRS database
 <EvenR> in GDAL 1.8.0, a lot of TOWGS84 have been added by taking into
 account the preferred datum shift from the EPSG database
 <nIRV> omg, it actually works
 <nIRV> I created a custom crs using the indian 1960 48n definition and
 adding the +towgs84 bit, et voila
 <EvenR> you can point to http://trac.osgeo.org/gdal/changeset/18978 which
 is the changeset during GDAL 1.8.0 where the datum shift logic has been
 improved

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Ticket URL: <http://trac.osgeo.org/qgis/ticket/3645>
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