I am currently looking at upgrading from GDAL 2.x to GDAL 3.x. Most of my
software tests pass, but I have a few failing because a transform from WGS84 to
WGS84 is flipping the axes on transformed geometries.
I have a recollection of reading about GDAL 3 (or PROJ 6) resulting in axis
swapping in some cases, but can't find the discussion/Github issue again.
The two SRS objects appear identical, and seem to report the same axis order,
but a point at (1, 0) gets transformed to (0, 1) - Python code below:
>>> from_proj = ds.GetLayer().GetSpatialRef()
>>> to_proj = osr.SpatialReference()
>>> to_proj.ImportFromEPSG(4326)
>>> to_proj.GetAxisName(None, 0)
'Geodetic latitude'
>>> to_proj.GetAxisName(None, 1)
'Geodetic longitude'
>>> from_proj.GetAxisName(None, 0)
'Geodetic latitude'
>>> from_proj.GetAxisName(None, 1)
'Geodetic longitude'
>>> xform = osr.CoordinateTransformation(from_proj, to_proj)
>>> xform.TransformPoint(1.0, 0.0)
(0.0, 1.0, 0.0)
If I follow from_proj back to its origin, it is also imported by importing from
an EPSG code, which is again 4326:
>>> projection = osr.SpatialReference()
>>> projection.ImportFromEPSG(epsg)
>>> temp_ds = gdal.GetDriverByName('Memory').Create('', 0, 0, 0)
>>> layer = temp_ds.CreateLayer(name, projection, geom_type=geom_type)
The two SRS objects appear identical when exported to WKT:
>>> from_proj.ExportToWkt()
'GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS
84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AXIS["Latitude",NORTH],AXIS["Longitude",EAST],AUTHORITY["EPSG","4326"]]'
>>> to_proj.ExportToWkt()
'GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS
84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AXIS["Latitude",NORTH],AXIS["Longitude",EAST],AUTHORITY["EPSG","4326"]]'
And if I re-import the SRSes from those WKT strings, the transform starts to
behave:
>>> from_proj_reimported = osr.SpatialReference();
>>> from_proj_reimported.ImportFromWkt(from_proj.ExportToWkt())
>>> to_proj_reimported = osr.SpatialReference();
>>> to_proj_reimported.ImportFromWkt(to_proj.ExportToWkt())
>>> new_xform = osr.CoordinateTransformation(from_proj_reimported,
>>> to_proj_reimported)
>>> new_xform.TransformPoint(1.0, 0.0)
(1.0, 0.0, 0.0)
How are these two SRS objects ending up with flipped axes, how can I actually
tell that the axes are flipped, and what do I need to do to un-flip them (short
of exporting and reimporting every time I use them)?
Dr. Daniel Evans
Software Developer
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