geotiff: gds chunked gpu chunk task casts to declared dtype (#1909) by brendancol · Pull Request #1918 · xarray-contrib/xarray-spatial

brendancol · 2026-05-15T13:27:07Z

Summary

Fixes #1909. The GDS chunked GPU read path (_read_geotiff_gpu_chunked_gds in xrspatial/geotiff/_backends/gpu.py) declared the dask graph dtype as float64 whenever the source had an in-range integer nodata sentinel, matching the CPU dask path's always-promote contract from #1597. The per-chunk _chunk_task ran the eager-style _apply_nodata_mask_gpu which only promotes when a sentinel pixel actually hits, so chunks with no sentinel hit returned the raw source dtype while the graph advertised float64 -- a silent declared/actual dtype mismatch.

Reproducer (pre-fix)

import tempfile, numpy as np
from xrspatial.geotiff import to_geotiff, read_geotiff_gpu

arr = np.arange(40, dtype=np.uint16).reshape(5, 8) + 100  # no 9999 pixel
with tempfile.NamedTemporaryFile(suffix='.tif', delete=False) as f:
    tmp = f.name
to_geotiff(arr, tmp, compression='none', nodata=9999)

rdg = read_geotiff_gpu(tmp, chunks=4)
print(rdg.data.dtype)             # float64
print(rdg.data.compute().dtype)   # uint16  <-- silent mismatch

Fix

Move the declared_dtype computation above _chunk_task so the closure can capture it, then cast arr to declared_dtype before returning. The cast is gated on arr.dtype != declared_dtype to skip the no-op astype(copy=True) allocation (mirrors the #1624 fix on the CPU dask path).

Backend parity matrix (post-fix)

uint16 file, nodata=9999 declared, no sentinel pixel hits:

backend	declared	computed
numpy (`open_geotiff`)	uint16	uint16
cupy (`read_geotiff_gpu`)	uint16	uint16
dask+numpy (`read_geotiff_dask(chunks=...)`)	float64	float64
dask+cupy (`read_geotiff_gpu(chunks=...)`)	float64	float64

The eager paths only promote when a sentinel pixel hits (preserves source dtype for memory-budgeted users); the dask paths always promote so chunk concatenation cannot silently downcast (#1597 contract). Both contracts are valid; the bug was the dask+cupy graph declaring one contract and the chunks returning the other.

Test plan

6 new regression tests in xrspatial/geotiff/tests/test_chunked_gpu_declared_dtype_1909.py:
- declared vs computed parity
- CPU/GPU dask declared-dtype agreement
- eager paths preserve source dtype
- no-nodata round-trip stays at source dtype
- explicit dtype= kwarg threads through
- sentinel-hit float64 promotion still NaN-masks correctly
Existing test_gds_chunked_gpu_parity_1896.py and test_dask_cupy_combined.py pass (11 tests).
Broad geotiff suite (xrspatial/geotiff/tests/): 2875 passed, 7 skipped. The pre-existing failures in test_predictor2_big_endian_gpu_1517.py (AttributeError: module 'xrspatial.geotiff' has no attribute 'read_to_array' after the geotiff: split __init__.py into per-backend modules with shared validation #1813 modular refactor renamed it to _read_to_array) and test_size_param_validation_gpu_vrt_1776.py (tile_size=4 rejected by stricter _validate_tile_size_arg) exist on main and are unrelated to this fix.

Detection

Caught by the deep-sweep metadata propagation audit on 2026-05-15. Cat 4 (dtype/nodata semantics) and Cat 5 (backend-inconsistent metadata).

The GDS chunked GPU read path declared the dask graph dtype as float64 whenever the source had an in-range integer nodata sentinel, matching the CPU dask path's always-promote contract from #1597. The per-chunk _chunk_task ran the eager-style _apply_nodata_mask_gpu which only promotes when a sentinel pixel actually hits, so chunks with no sentinel hit returned the raw source dtype while the graph advertised float64 -- a silent declared/actual dtype mismatch. The fix moves the declared_dtype computation above _chunk_task so the closure can capture it, then casts arr to declared_dtype before returning. The cast is gated on arr.dtype != declared_dtype to skip the no-op astype(copy=True) allocation (mirrors the #1624 fix on the CPU dask path). 6 regression tests in test_chunked_gpu_declared_dtype_1909.py cover declared vs computed parity, CPU/GPU dask declared-dtype agreement, eager paths preserving source dtype, no-nodata round-trip, explicit dtype= kwarg, and sentinel-hit float64 promotion. Caught by the deep-sweep metadata propagation audit on 2026-05-15.

Copilot

Pull request overview

This PR fixes a declared-vs-computed dtype mismatch in the GeoTIFF dask+cupy GDS chunked read path, ensuring that each computed chunk is cast to the same dtype that the dask graph advertises (notably for integer rasters with an in-range nodata sentinel).

Changes:

Compute declared_dtype before defining the GDS _chunk_task, and cast each chunk result to declared_dtype (skipping no-op casts) in xrspatial/geotiff/_backends/gpu.py.
Add regression tests intended to cover declared vs computed dtype parity and related backend behaviors.
Update the .claude sweep/audit state log to record the new finding and fix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
`xrspatial/geotiff/_backends/gpu.py`	Ensures GDS chunk tasks cast outputs to the dask graph’s declared dtype to avoid silent dtype mismatches.
`xrspatial/geotiff/tests/test_chunked_gpu_declared_dtype_1909.py`	Adds regression tests around chunked GPU dtype declaration/computation parity and nodata/dtype interactions.
`.claude/sweep-metadata-state.csv`	Updates audit metadata to reflect the #1909 finding and verification notes.

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+    to_geotiff,
+)
+
+cupy = pytest.importorskip("cupy")


+def test_chunked_gpu_declared_dtype_matches_computed(uint16_no_sentinel_path):
+    """Declared dask graph dtype must equal the computed chunk dtype."""
+    da = read_geotiff_gpu(str(uint16_no_sentinel_path), chunks=4)
+    declared = da.data.dtype
+    computed = da.data.compute().dtype


+    assert da.data.dtype == np.float64
+    computed = da.data.compute()
+    assert computed.dtype == np.float64
+    assert np.isnan(computed[0, 0])


Address copilot review on #1918: - Use _gpu_only gate (cupy + cupy.cuda.is_available) instead of bare importorskip so the suite skips on hosts without CUDA, matching test_gds_chunked_gpu_parity_1896.py. - Call _read_geotiff_gpu_chunked_gds directly with a tiled fixture so the GDS chunked path is exercised regardless of kvikio availability. read_geotiff_gpu(chunks=...) only enters the GDS path when _gds_chunk_path_available qualifies; the previous fixture used a stripped file, so the test asserted a property that already held on the CPU-dask + upload fallback. - Use computed.get() before np.isnan so the host-side NumPy check is unambiguous on cupy buffers.

Copilot AI review requested due to automatic review settings May 15, 2026 13:27

github-actions Bot added the performance PR touches performance-sensitive code label May 15, 2026

Copilot started reviewing on behalf of brendancol May 15, 2026 13:27

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Copilot AI reviewed May 15, 2026

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brendancol merged commit b176169 into main May 15, 2026
10 of 11 checks passed

brendancol deleted the deep-sweep-metadata-geotiff-2026-05-15 branch May 27, 2026 14:50

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geotiff: gds chunked gpu chunk task casts to declared dtype (#1909) - #1918

geotiff: gds chunked gpu chunk task casts to declared dtype (#1909)#1918
brendancol merged 2 commits into
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deep-sweep-metadata-geotiff-2026-05-15

brendancol commented May 15, 2026

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brendancol commented May 15, 2026

Summary

Reproducer (pre-fix)

Fix

Backend parity matrix (post-fix)

Test plan

Detection

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Pull request overview

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