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fix: embed EPSG in Zarr attrs for TiTiler CRS detection #46

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fix: embed EPSG in Zarr attrs for TiTiler CRS detection #46

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wietzesuijker
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TiTiler defaults to EPSG:4326 when ds.rio.crs returns None after Zarr I/O, causing validation errors on native UTM coordinates (e.g., treating 600000 meters as longitude degrees).

Solution
Embed proj:epsg and proj:code in dataset attrs so rioxarray reconstructs CRS after Zarr write/read cycle.

Changes

  • Add _embed_crs_in_attrs() helper
  • Call from prepare_dataset_with_crs_info()
  • Add validation test test_crs_fix.py

Impact

  • Fixes TiTiler 500 errors on UTM datasets
  • Enables correct tile rendering in STAC browser

j08lue
j08lue requested changes Oct 3, 2025
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Pls use the existing tests dir and refactor this to use pytest.

test_crs_fix.py Outdated
Comment on lines 46 to 47
assert "proj:epsg" in ds_prepared.attrs, "proj:epsg not found in dataset attrs"
assert "proj:code" in ds_prepared.attrs, "proj:code not found in dataset attrs"
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@emmanuelmathot, do we have attribute validation implemented somewhere already, e.g. using pydantic?

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Not that I'm aware of. The focused assertions here work for CRS metadata validation, but if there's a project-wide schema validation approach, I'd be happy to align with that!

@wietzesuijker wietzesuijker requested a review from j08lue October 3, 2025 15:20
@wietzesuijker
fix: embed EPSG in Zarr attrs for TiTiler CRS detection
a1e7ebf 
TiTiler defaults to EPSG:4326 when ds.rio.crs is None, causing validation
errors on UTM coordinates. Extract helper to embed proj:epsg in attrs so
rioxarray reconstructs CRS after Zarr I/O.
@emmanuelmathot
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TiTiler defaults to EPSG:4326 when ds.rio.crs returns None after Zarr I/O, causing validation errors on native UTM coordinates (e.g., treating 600000 meters as longitude degrees).

How do you reproduce that? in titiler-eopf, the xarray open_dataset with decode_coordinates uses the grid_mapping and the crs is fine. I am curious to understand the context.

proj:epsg and proj:code are not standard, just copied from STAC. rioxarray does not read them: https://corteva.github.io/rioxarray/stable/getting_started/crs_management.html

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@emmanuelmathot emmanuelmathot Awaiting requested review from emmanuelmathot

@j08lue j08lue Awaiting requested review from j08lue

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3 participants
@wietzesuijker @emmanuelmathot @j08lue