GEOSGeometry.transform() silently no-ops when GDAL isn't available or srid is None

[Robert Coup]

GEOSGeometry.transform() uses the GDAL library to re-project geometries. If GDAL is not available however, it silently does nothing.

Geodjango-Users discussion thread: ​http://groups.google.com/group/geodjango/browse_thread/thread/788cafdbd592d617

Current behaviour if GDAL is unavailable:

• .transform(clone=False) (the default) does nothing
• .transform(clone=True) returns None

Also related:

• .transform(clone=False) (the default) called on a geometry where .srid is None does nothing
• .transform(clone=True) called on a geometry where .srid is None returns None

Since transform(clone=False) (the default) mutates the geometry, it should raise an exception if it can't do what the caller asked.

The attached patch:

• short-circuits re-projection if the source and destination SRIDs match
• makes .transform() raise a GEOSGeometry.Error if GDAL isn't available
• adds tests around the new behaviour
• adds a FutureWarning if the srid of the geometry is None or <0, pointing out that in 1.5 the behaviour will change an error will be raised.
• adds some docs, including notes to the backwards-incompatibilities for 1.3

The backwards incompatible behaviour change is being introduced because:

• .transform() no-op'ing if source & destination SRIDs don't match is NOT what the caller wants - it is in all cases a bug.
• It's unlikely the user was manually checking either the return value (clone=True) or the geometry's srid (clone=False) and raising their own exception, the more common case would be to assert on HAS_GDAL.

[Robert Coup]

initial patch

[Robert Coup]

My documentation/rest-fu isn't strong, so probably worth a look there, and i'm not sure whether the notes for the release are all in the right places :)

[jbronn]

Updated

[jbronn]

(In [15025]) Fixed #13788 -- GEOSGeometry.transform no longer silently no-ops when GDAL isn't available. Thanks, Rob Coup.

[Jacob]

Milestone 1.3 deleted