synchronize QGIS' SRS definitions with GDAL's 1.8.0 SRS database
|Reported by:||nirvn||Owned by:||jef|
|Priority:||critical: causes crash or data corruption||Milestone:||Version 1.7.0|
|Must Fix for Release:||No||Platform:||All|
|Platform Version:||Awaiting user input:||no|
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