Emit fresh grid metadata and propagate _FillValue through reproject() and merge()#1462
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brendancol merged 1 commit intomainfrom May 4, 2026
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Three small follow-ups to PR #1446 in `xrspatial/reproject/__init__.py`: - `reproject()` and `merge()` re-emit `attrs['transform']` and `attrs['res']` for the new output grid instead of dropping them. The transform uses the rasterio 6-tuple convention `(res_x, 0.0, left, 0.0, -res_y, top)`. The geotiff reader does not itself write these attrs, so there is no in-repo convention to match and the rasterio form is used as the default. - `merge()` uses `_find_spatial_dims` instead of assuming the last two dims are spatial, both when collecting per-raster shapes and when building the output coords. - Both functions copy the resolved nodata value into `_FillValue` when the input set `_FillValue`. Inputs that did not set `_FillValue` get no `_FillValue` on output. Tests in `TestMetadataPreservation` cover the fresh transform/res values, absence-of-input behaviour, `_find_spatial_dims` use with lat/lon dims, and `_FillValue` round-trip for both functions.
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Closes #1458.
Follow-up to #1446 covering three small metadata items in
xrspatial/reproject/__init__.py.Changes
Fresh
transformandreson output. Bothreproject()andmerge()previously poppedtransformandresbecause the input values described the old grid. The output grid is fully known from_compute_output_grid(returnsres_x,res_y, andbounds), so we now emit:attrs['res'] = (res_x, res_y)attrs['transform'] = (res_x, 0.0, left, 0.0, -res_y, top)— rasterio 6-tuple convention.The geotiff reader in this repo does not emit
transformorresintoattrsitself, so there was no in-repo convention to match. The rasterio form is the standard one external code expects.merge()honours_find_spatial_dims. The helper at line 63 already exists andreproject()uses it.merge()was hardcoded todims[-2]anddims[-1]in two places. Both now call_find_spatial_dims, so inputs withlat/londims (or other non-y/x layouts) work correctly._FillValuepropagation._detect_nodatareads_FillValueas a fallback nodata key, but neither output set_FillValue. When the input has_FillValue, the output now gets the resolved nodata in bothnodataand_FillValue. When the input has no_FillValue, the output stays clean.Tests
Added eight tests in
TestMetadataPreservation:reproject()andmerge()transformandresemitted even when the input had neithermerge()succeeds withlat/londims and preserves them on output_FillValueround-trips through both functions when the input sets it, and stays absent when the input does notTwo existing tests that asserted
transform/reswere dropped have been updated to assert that the new (fresh) values differ from the stale input values.Test plan
pytest xrspatial/tests/test_reproject.py -x(188 passed)