geotiff: GPU stripped windowed read of non-georef TIFF emits float64 coords (regression of #1710) #1753

Summary

open_geotiff(path, gpu=True, window=...) on a TIFF with no GeoTIFF tags (no ModelPixelScale / ModelTiepoint / GeoKeyDirectory) returns float64 coords like [-0.5, -1.5, ...] synthesised from the default unit GeoTransform, instead of integer pixel coords [0, 1, 2, ...] that the eager numpy and dask paths emit.

This was fixed in #1710 for the eager numpy path (open_geotiff), the dask path (read_geotiff_dask), and the tiled GPU path (_gpu_apply_window_band). The stripped-fallback branch in read_geotiff_gpu was missed.

Reproduction

import numpy as np
from xrspatial.geotiff import open_geotiff
from xrspatial.geotiff._writer import write

arr = np.arange(64, dtype=np.float32).reshape(8, 8)
path = "/tmp/no_georef.tif"
write(arr, path, compression='none', tiled=False)  # stripped, no georef

eager = open_geotiff(path, window=(0, 0, 4, 4))
dask = open_geotiff(path, chunks=4, window=(0, 0, 4, 4))
gpu = open_geotiff(path, gpu=True, window=(0, 0, 4, 4))

print(eager.y.dtype, eager.y.values)   # int64 [0 1 2 3]
print(dask.y.dtype, dask.y.values)     # int64 [0 1 2 3]
print(gpu.y.dtype, gpu.y.values)       # float64 [-0.5 -1.5 -2.5 -3.5]  <- WRONG

The eager / dask / tiled-GPU paths all guard on geo_info.has_georef. The stripped-GPU fallback in read_geotiff_gpu only checks t is None, which is never true for non-georef files because _extract_transform returns a default GeoTransform() instance with has_georef=False. The default transform has pixel_width=1.0, pixel_height=-1.0, so the PixelIsArea branch produces (c0 + 0.5) * 1.0 + 0 and (r0 + 0.5) * -1.0 + 0 -> [-0.5, -1.5, ...].

Affected backends

• gpu=True stripped reads with window=...
• gpu=True, chunks=... stripped reads with window=...

The tiled-GPU and CPU paths are not affected.

Severity

HIGH (Cat 2 - coords preservation). Coord dtype changes silently between the input full-read (int64) and the windowed-read on the GPU backend (float64), breaking backend parity. Downstream coord-based math (clipping, interp, xarray slicing) gets different answers depending on which backend is active.

Test failures

xrspatial/geotiff/tests/test_no_georef_windowed_coords_1710.py:

• TestGpuWindowedCoords::test_windowed_read_integer_coords
• TestGpuWindowedCoords::test_dask_cupy_windowed_integer_coords
• TestBackendParity::test_dtype_parity_windowed