Better error handling and/or error reporting when Proj.4 datum shifting files are not found
|Reported by:||springmeyer||Owned by:||jbronn|
|Severity:||Normal||Keywords:||proj4, datum shifing, geodjango-basic-apps, postgis, 900913, projections|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
A very common install problem for new users to GeoDjango is to use a package management system for installing proj which does not include the Proj.4 datum shifting files (A key question is do any packager of proj include these files?). Or a user does a source install of proj and misses the instructions here: http://geodjango.org/docs/install.html#proj-4 and fails to manually install the additional files.
The impact of the lacking files is often first seen for new users who download one of the apps that uses the OSMGeoAdmin from http://code.google.com/p/geodjango-basic-apps/. Without a use of GeoDjango like this that does transformations between Google Spherical Mercator projection (http://spatialreference.org/ref/user/google-projection/) and another projection in a different datum, this installation problem might not surface for many users.
OSMGeoAdmin uses GDAL to do reprojection of data into SRID 900913 for the Admin OpenLayers map and then uses the spatial database backend to reproject the data back to the native SRID after the save() method is called.
With a PostGIS backend the spatial data is sent to in the database without proper reprojection due to the missing files with no error warning of the missing files needed. The geometry therefore misses the validation check at the form level, such that and error is throw by a GEOS error check only after finding corrupt coordinates which is not super intuitive as to the original problem:
Error encountered checking Geometry returned from GEOS C function "GEOSGeomFromHEX_buf"