Property proj:epsg is remapped to proj:code

[dwest77a]

I've noticed that an item with proj:epsg set to some value (e.g 32621) is remapped/altered at some point by the pystac client to read proj:code = EPSG:32621 instead. Is this a recent change by the client, or being caused by some other package/extension? Thanks

[dwest77a]

An example can be found when loading https://api.stac.ceda.ac.uk/collections/cci_openeo_test/items/ndvi-example-stac-item1

[gadomski]

Yup, this is intentional as a part of the upgrade to v2.0 of the projection extension: https://github.com/stac-utils/pystac/blob/795befab413b4ea38afce314815801a0ab3db6b7/pystac/extensions/projection.py#L480-L481

There's ways to (de)serialize pystac items while skipping that migration path but it's often awkward. Unfortunately the documentation is pretty thin on this point -- one small example is the migrate argument here: https://pystac.readthedocs.io/en/stable/api/pystac.html#pystac.STACObject.from_dict.

In general, pystac does not have any fidelity guarantees for (de)serialization.

[jsignell]

Just want to point out that the stac_extensions list is also updated on the item to point to projection extension v2 so the returned item is valid.

[dwest77a]

Ok thanks, sounds like I may need to remove one or both of the extensions applied to the item, as I need the proj:epsg property for use with OpenEO client - this is a required parameter for all items.

[gadomski]

Can you point me to where that's defined? It'd be good to update that, if possible -- you won't be the only person who runs into this.

Also, if proj v2 support was added in pystac v1.12.0, so you could require pystac < 1.12 in your project.

[dwest77a]

Is pystac v1.12 required for the projections v2 support? I have encountered the issue that using the v2 specification does not work for the latest openeo-processes-dask version, which requires pystac < 1.12.

The v1.1.0 specification and syntax does work for openeo-processes-dask 2025.7.1, but possibly for the reasons above does not work with v2.0.0 as the proj:code syntax is not handled correctly.

[dwest77a]

Following up on this, it looks like pystac v1.12 is required for v2 specification support, which means it is not yet supported in openeo.

[gadomski]

Is pystac v1.12 required for the projections v2 support?

pystac v1.12 can read items w/ projection extension v2 just fine, you just won't get any of the Python API for the extension (e.g. item.ext.proj.code). In general, you can always get to "unsupported" attributes via extra_fields, e.g.:

item.extra_fields["proj:code"]