Fix read_vrt dropping SimpleSource <NODATA>0</NODATA> (#1655)#1663
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The per-source nodata fallback used `src.nodata or nodata`, and Python treats `0.0` as falsy. A SimpleSource that declared `<NODATA>0</NODATA>` silently picked up the band-level `<NoDataValue>` (or `None` when none was set), so pixels equal to 0.0 in the source file survived as valid data instead of being masked to NaN. The in-code comment described the behaviour as "backward compatibility" but the result is silent data corruption on VRTs that mosaic sources using 0 as a sentinel (a common remote-sensing convention). Switch to an explicit `is not None` check so a legitimate zero sentinel survives the fallback. Add `test_vrt_source_nodata_zero_1655.py` covering five cases: source NODATA=0 with no band fallback, integer XML literal, non-zero unchanged, band-level NoDataValue=0 still honoured when no per-source NODATA is set, and per-source precedence over a different band-level sentinel.
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Summary
Closes #1655.
xrspatial.geotiff._vrt.read_vrtsilently treated<NODATA>0</NODATA>on aSimpleSourceas if the element were absent. The per-source nodata fallback usedsrc.nodata or nodata; Python evaluates0.0 or <anything>to<anything>because0.0is falsy. The in-code comment described the behaviour as "backward compatibility" but the result is silent data corruption on VRTs that mosaic sources using 0 as a sentinel (a common remote-sensing convention for unsigned imagery).Switch to an explicit
is not Nonecheck so a legitimate zero sentinel survives the fallback. The behaviour now matches the per-source nodata semantics that GDAL applies.Test plan
test_vrt_source_nodata_zero_1655.py(5 tests): source NODATA=0 with no band fallback, integer XML literal<NODATA>0</NODATA>, non-zero unchanged, band-level<NoDataValue>0</NoDataValue>still honoured, per-source NODATA precedence over a different band sentinel.Notes
Found via
/deep-sweepaccuracy pass 19 on thegeotiffmodule. State file updated in the same commit.