to_wkt fails with WKT1_GDAL for EPSG:4979

[glostis]

Hi,

I'm using your excellent CRS compatibility guide to convert pyproj.CRS objects into rasterio.crs.CRS objects in order to properly encode the CRS of some images which happen to be DEMs - I therefore want the vertical component of the CRS to be correct.

Specifically, I need to write a GeoTIFF with CRS EPSG:4979, and another one with CRS EPSG:4326+5773 (thanks @snowman2 for the great info you gave me in #630 about CompoundCRS by the way!).

I have rasterio 1.1.8 (rasterio.__gdal_version__ 2.4.4) and pyproj 2.6.1.post1 both installed from their respective PyPI wheels.

The following snippet:

import rasterio
import rasterio.crs
from pyproj.crs import CRS
from pyproj.enums import WktVersion

rasterio.crs.CRS.from_wkt(CRS("EPSG:4326+5773").to_wkt(WktVersion.WKT1_GDAL))
rasterio.crs.CRS.from_wkt(CRS("EPSG:4979").to_wkt(WktVersion.WKT1_GDAL))

works for EPSG:4326+5773, but fails for EPSG:4979 with the following traceback:

Traceback (most recent call last):
  File "t.py", line 7, in <module>
    rasterio.crs.CRS.from_wkt(CRS("EPSG:4979").to_wkt(WktVersion.WKT1_GDAL))
  File "/home/glostis/.venv/multidem/lib/python3.8/site-packages/rasterio/crs.py", line 462, in from_wkt
    obj._crs = _CRS.from_wkt(wkt, morph_from_esri_dialect=morph_from_esri_dialect)
  File "rasterio/_crs.pyx", line 383, in rasterio._crs._CRS.from_wkt
ValueError: A string is expected

If I remove the WktVersion.WKT1_GDAL from the above snippet, the conversion to a rasterio.crs.CRS works in both cases - or at least the code doesn't crash.

Can I safely remove WktVersion.WKT1_GDAL and still expect my conversion to be correct? Do you know why the conversion for EPSG:4979 fails in the first case? Is it because it's a 3D CRS?

Thanks!

[snowman2]

Do you know why the conversion for EPSG:4979 fails in the first case? Is it because it's a 3D CRS?

When using the projinfo command I see this output:

$ projinfo EPSG:4979 -o WKT1:GDAL
WKT1:GDAL string:
Error when exporting to WKT1:GDAL: WKT1 does not support Geographic 3D CRS.

Can I safely remove WktVersion.WKT1_GDAL and still expect my conversion to be correct?

The only way to for it to be safe would be to use GDAL 3+ with PROJ 6+. Otherwise, you will need to proceed with caution and I would recommend doing more validation to be sure everything worked as expected.

[glostis]

I see, thank you for the explanation!