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VRTWarpedDataset::IRasterIO(): honour requested resampling on rescaled reads #15427

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VRTWarpedDataset::IRasterIO(): honour requested resampling on rescaled reads #15427

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22 changes: 22 additions & 0 deletions autotest/gdrivers/vrtwarp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -705,6 +705,28 @@ def test_vrtwarp_irasterio_optim_three_band():
)


###############################################################################
# Test that VRTWarpedDataset::IRasterIO() honours the requested resampling
# when reading the whole image at a reduced resolution


def test_vrtwarp_irasterio_optim_rescaled_resampling():

src_ds = gdal.Translate("", "data/byte.tif", format="MEM", width=1000)
warped_vrt_ds = gdal.Warp("", src_ds, format="VRT")

with gdaltest.config_option("GDAL_VRT_WARP_USE_DATASET_RASTERIO", "NO"):
expected_data = warped_vrt_ds.ReadRaster(
buf_xsize=100, buf_ysize=10, resample_alg=gdal.GRIORA_Average
)
assert (
warped_vrt_ds.ReadRaster(
buf_xsize=100, buf_ysize=10, resample_alg=gdal.GRIORA_Average
)
== expected_data
)


###############################################################################
# Test VRTWarpedDataset::IRasterIO() code path

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5 changes: 4 additions & 1 deletion frmts/vrt/vrtwarped.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1959,7 +1959,10 @@ CPLErr VRTWarpedDataset::IRasterIO(

if (nBufXSize != nXSize || nBufYSize != nYSize)
{
if (!bWholeImage || !GDALTransformHasFastClone(psWO->pTransformerArg))
// The rescaled warp below ignores the requested resampling
if (!bWholeImage ||
psExtraArg->eResampleAlg != GRIORA_NearestNeighbour ||
!GDALTransformHasFastClone(psWO->pTransformerArg))
{
return GDALDataset::IRasterIO(eRWFlag, nXOff, nYOff, nXSize, nYSize,
pData, nBufXSize, nBufYSize, eBufType,
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