ENH: Add WKT format support

[snowman2]

Closes #977

[coveralls]

Coverage increased (+0.04%) to 87.666% when pulling fafb779 on snowman2:wkt2 into 137853e on Toblerity:maint-1.9.

[mwtoews]

@snowman2 Fiona 1.9 has been updated to require GDAL >=3.1 (see b4dcc40), so a few simplifications could be made throughout this PR. I can review this when ready.

[snowman2]

@mwtoews, I think this is ready for a review.

[mwtoews]

This error should somehow also describe wkt_version, e.g. fiona._crs.crs_to_wkt(target_crs, wkt_version="abc") will raise an error that makes no mention of a potentially bad wkt_version value.

Not sure if it's possible to capture possible invalid wkt_version values earlier, or if that's a bad idea, as other values work, e.g. wkt_version="WKT2".

[snowman2]

I am wondering if we could capture the underlying GDAL error message and raise it here. That may have more information about it.

[snowman2]

For now, I am adding the supported WKT versions to the error message on error.

[mwtoews]

there are a few ways to capture an error message, like this

Fiona/fiona/ogrext.pyx

Lines 1512 to 1516 in 9c8fe73

	try:
	exc_wrap_int(
	OGR_L_SetAttributeFilter(cogr_layer, <const char*>where_c))
	except CPLE_AppDefinedError as e:
	raise AttributeFilterError(e) from None

[snowman2]

Thanks!

Current error message:

fiona.errors.CRSError: Invalid input to create CRS: EPSG:4326. Please choose a different WKT version (WKT2 is recommended): WKT1 | WKT1_GDAL | WKT1_ESRI | WKT2 | WKT2_2018 | WKT2_2015. GDAL ERROR: Unsupported value for FORMAT

[mwtoews]

Useful error capture, as sometimes WKT1_GDAL will be specified, but the error message would contain (e.g.) "GDAL ERROR: PROJ: proj_as_wkt: Unsupported conversion method: Lambert Conic Conformal (2SP Michigan)" as the chosen wkt format is incompatible.

[mwtoews]

Thanks, looks great! Last request is to add an entry to CHANGES.txt (in the "New features" section), then I'll merge it after a few days (in case there is any further review by others).

[mwtoews]

Thanks for the time an patience putting this together! The last CI failure is unrelated and is fixed with 7fa6bcc

[snowman2]

Thanks @mwtoews 👍

[rouault]

for the Fiona API, I would suggest using WKT2_2019 which is the canonical name and remap that to WKT2_2018 when passing it to GDAL for compatibility with early GDAL 3.1 (WKT2_2019 was added in GDAL 3.2)