Add GPU COG overview support (#1150)#1174
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write_geotiff_gpu now accepts cog, overview_levels, and overview_resampling. Overviews are block-reduced and compressed on GPU, then assembled into COG layout. to_geotiff() passes the new params through to the GPU path.
Tests cover resampling methods (mean, nearest, mode, min, max, median), multi-level overviews, auto-generation, round-trip value preservation, public API dispatch, and GPU/CPU parity for block-reduce.
New docs/source/reference/geotiff.rst covers the public I/O functions. README feature matrix now lists write_geotiff_gpu and shows COG overview usage examples.
Covers automatic and explicit overview levels, resampling methods, and round-trip verification. Self-contained with synthetic data.
GDAL and rasterio use TIFF tag 254 (NewSubfileType = 1) to identify overview sub-IFDs. Without it, overviews are written correctly but invisible to GDAL-based tools. Verified: rasterio and gdalinfo now see both overview levels, and pixel values match GDAL's own COG output to within float32 rounding (max relative error < 0.0001%).
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Summary
write_geotiff_gpu()now acceptscog,overview_levels, andoverview_resampling. Overviews are block-reduced and compressed on GPU, then written in COG layout (IFDs first, pixel data after).to_geotiff()passes overview params through to the GPU path, so CuPy arrays get COG output without CPU fallback.Test plan
pytest xrspatial/geotiff/tests/test_cog.py-- 25 tests (9 existing + 16 new), all passCloses #1150