geotiff: synthesize WKT for citation-only user-defined CRSes (#1930)#2054
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After the oracle's axis-order normaliser landed, the eager / dask JPEG xfails resolved cleanly. The GPU and dask+GPU paths still xfailed because the GPU JPEG-YCbCr decoder is not implemented. Address both: * GPU module: introduce ``_GPU_CPU_FALLBACK`` to mark fixtures whose codec is genuinely not implemented on the GPU. The parity test routes those through ``on_gpu_failure='auto'`` instead of ``'strict'``, which exercises the documented CPU fallback contract. The fallback yields a CPU-decoded DataArray that the oracle compares cleanly against the rasterio reference. JPEG cell now PASSES. * dask+GPU module: move JPEG from ``_DASK_GPU_SKIPS`` to ``_INTENTIONAL_SKIPS``. The chunked GPU path cannot fall back per chunk -- the decode error surfaces at ``.compute()`` time regardless of ``on_gpu_failure`` mode, and there is no foreseeable fix short of implementing nvCOMP JPEG-YCbCr decode. Plain skip is more honest than xfail(strict=True). Result: GPU and dask+GPU modules carry no JPEG xfails. The only remaining corpus xfails are the four ``crs_citation_only`` entries across the four backend modules, owned by the parallel PR #2054.
Closes the citation-only CRS parity gap that every phase-3 backend module flagged. The crs_citation_only fixture in the golden corpus carries a user-defined geographic CRS (no EPSG, no WKT in the citation) and the reader was decoding it only into the deprecated geog_citation / datum_code / angular_units attrs. attrs['crs_wkt'] stayed None, so the oracle's _candidate_crs returned None on the candidate side and compare_to_oracle failed. This change adds _synthesize_user_defined_wkt to _geotags.py. When the file declares a user-defined geographic CRS and exposes the ellipsoid (semi_major plus semi_minor or inv_flattening) and the angular-units GeoKeys, the helper feeds those parameters to pyproj.CRS.from_dict and stamps the resulting WKT on attrs['crs_wkt']. The synthesis fails closed (returns None) when pyproj is missing, when there is no semi_major, or when the ellipsoid shape is ambiguous, so the existing deprecated-attrs path stays in place. Projected user-defined CRSes (ModelTypeProjected with ProjectedCSType == 32767) are not yet reconstructible from GeoKeys alone -- they need the GeogPrime / Projection parameters that the corpus does not exercise -- so the helper returns None for that case. Drops the crs_citation_only entry from _PARITY_GAPS in each of the four phase-3 backend modules (eager numpy, dask numpy, GPU, dask+GPU). xfail(strict=True) flips to a real failure when the test starts passing, so the fix and the entry cleanups have to land together. Each module's top-of-file docstring moves the citation entry from "Real parity gaps" to "Resolved gaps", mirroring the masked-nodata fix from PR #2046. Adds unit tests for _synthesize_user_defined_wkt in test_user_defined_crs_wkt_1632.py: the sphere case (the citation fixture shape), the oblate ellipsoid case, the projected-CRS skip path, and the missing-ellipsoid skip path. Adds end-to-end fixture tests in test_oracle.py for attrs['crs_wkt'] stamping, PROJ-dict equality with the rasterio reference, and compare_to_oracle round-trip. After the fix the four phase-3 backend modules report 115 passed, 8 skipped, 4 xfailed (the remaining JPEG axis-order gap). The full golden_corpus / corpus suite reports 253 passed, 8 skipped, 4 xfailed with no XPASS.
* Adds ``GEOKEY_GEOG_SEMI_MINOR_AXIS = 2058`` next to the other GeoKey ID constants and uses it in ``extract_geo_info`` instead of the raw int literal. Matches the existing convention for the semi-major-axis and inv-flattening keys. * Drops ``angular_units_code`` and ``geog_citation`` from ``_synthesize_user_defined_wkt``. The function never read them. PROJ's ``longlat`` always emits degrees, and the corpus has no radian-unit user-defined fixture; the docstring now calls that limit out so a future radian fixture forces a deliberate signature change rather than silently degrading the units. * Expands the docstring's "not handled" section to call out ``MODEL_TYPE_GEOCENTRIC`` (3) and unknown / zero model_type. Adds a ``test_synthesize_user_defined_wkt_geocentric_returns_none`` pin so a future change that promotes geocentric to a real proj_dict has to touch the test deliberately. Full corpus suite still reports 287 passed, 8 skipped, 4 xfailed (JPEG axis-order gap), 0 XPASS.
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Summary
_synthesize_user_defined_wkttoxrspatial/geotiff/_geotags.pyso the reader can build a canonical WKT for citation-only user-defined geographic CRSes from the ellipsoid and units GeoKeys, then stamp it onattrs['crs_wkt']. Closes the citation-only parity gap from geotiff: first-class backend parity contract with a golden test corpus #1930.crs_citation_onlyentry from_PARITY_GAPSin all four phase-3 backend modules (eager numpy, dask numpy, GPU, dask+GPU) and moves the entry from "Real parity gaps" to "Resolved gaps" in each module's docstring.compare_to_oracleround-trip.Test plan
pytest xrspatial/geotiff/tests/test_golden_corpus_*_1930.py xrspatial/geotiff/tests/golden_corpus/-> 253 passed, 8 skipped, 4 xfailed (remaining JPEG axis-order gap), 0 XPASS.pytest xrspatial/geotiff/tests/test_user_defined_crs_wkt_1632.py-> all green.pytest xrspatial/geotiff/tests/golden_corpus/test_oracle.py-> all green including the two new citation tests.Refs #1930.