CRS Axis Order issues with 1.8.9

Problem Description

When reading in: https://raw.githubusercontent.com/geopandas/geopandas/master/geopandas/tests/data/overlay/overlap/df1_df2_overlap-union.geojson

With previous versions of Fiona, the WKT string was read in as:

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"]]

However, currently (1.8.9) it is read in as:

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["Longitude",EAST],AXIS["Latitude",NORTH]]

Everything is mostly the same except for the axis order at the end.

I believe this is due to this line: https://github.com/Toblerity/Fiona/blob/960568d2fede452a042e5c9f315fb93e3cd56baa/fiona/_crs.pyx#L65

This is problematic for a couple of reasons:

1. It does not preserve the original WKT string/projection and mangles it
2. What if the user actually modified their data to be in the axis order mentioned in the WKT string? How would they tell Fiona that they did so?

Recommended Solution

Add an always_xy flag to crs_to_wkt() and only use it when creating a CRS to be used in the transformation. It would also be a good idea to add an always_xy flag to the transformation operations for the case where the user modified the underlying data to match the axis order specified in the CRS. For Fiona 1.8.x, the always_xy flag could be omitted from the transformation operations and just default to always_xy=True in crs_to_wkt()

Thoughts?

[snowman2]

@snowman2 thanks for opening that issue!

Not a problem! Looks like EPSG:4326 is the winner in this scenario and the fix is in GDAL, so no change needed in Fiona.

[jorisvandenbossche]

the GeoJSON spec, RFC 7946, says the CRS is the OGC’s CRS84 (which is explicitly long/lat order). FIona shouldn’t go against that.

Well, Fiona (or GDAL) does go against it. When you use RFC7946="YES", you actually get back EPSG:4326 … It’s only when not using the new spec that you get back CRS84 (well, you get back what is written into the “crs” field of the geojson file, but it is impossible to write EPSG:4326 in that field, as it always get converted to CRS84)