[gdal-dev] OGR GeoJSON transormation woes

Frank Broniewski hallo at frankbroniewski.com
Wed May 6 07:27:24 PDT 2020

Hi everybody,

I've written a small plugin for QGIS in which I am using OGR to 
transform GeoJSON from a Web API into a national CRS.
It used to work fine, but the changes introduced to axis ordering with 
the latest versions of GDAL introduced errors in my code. Things aren't 
anymore where they are supposed to be :-)

The GeoJSON I receive is in LON/LAT coordinate ordering:
"coordinates": [6.1409004235, 49.6127108119]

The projected coordinates in LUREF/EPSG:2169 are:
"coordinates": [ 78032.625859561609104, 75343.040142811907572 ]

An here is what I have tried so far:
# correctly transformed geometry X/Y (LUREF epsg:2169)
# used to perform the test
target_geom = ogr.CreateGeometryFromJson('{ "type": "Point", 
"coordinates": [ 78032.625859561609104, 75343.040142811907572 ] }')

# source geometry with LON/LAT coordinates
ogr_geom = ogr.CreateGeometryFromJson('{"coordinates": [6.1409004235, 
49.6127108119], "type": "Point"}')

source_srs = osr.SpatialReference()

target_srs = osr.SpatialReference()

transformation = osr.CoordinateTransformation(source_srs, target_srs)

# test if equal /w unittest
self.assertEqual(target_geom.ExportToWkt(), ogr_geom.ExportToWkt())

So basically I imported the GeoJSON, created a transformation and 
applied it to the input geometry. The last line is just a test, the 
output from the test is as followed:

- POINT (78032.6258595616 75343.0401428119)
+ POINT (75343.0401428119 78032.6258595616)

As you can see the transformed geometry still has the coordinate order 
mixed up, but the numbers are already right with 
OAMS_TRADITIONAL_GIS_ORDER. I have searched quite a bit, stumbled over 
https://gdal.org/tutorials/osr_api_tut.html but I am out of wits here now.

I mean, I can easily swap the input coordinates to match LAT/LON, but 
this seems rather hacky. There must be a way to achieve this with OGR, 
right? So any help here is greatly appreciated!


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