Fix #251.

Based closely on code provided by @lukesdm

Author: SpacemanPaul

odc/stac/_mdtools.py

@@ -505,13 +505,19 @@ def extract(self, md: Any) -> RasterGroupMetadata:
         # disabled that filter with `ignore_proj=True` option
         check_proj = has_proj_ext(item) and not c.ignore_proj
 
-        def _keep(kv: tuple[str, pystac.asset.Asset]) -> bool:
+        def _keep(kv: tuple[str, pystac.asset.Asset], check_proj: bool) -> bool:
             name, asset = kv
             if name in c.band_cfg:
                 return True
             return is_raster_data(asset, check_proj=check_proj)
 
-        data_bands = dicttoolz.itemfilter(_keep, item.assets)
+        data_bands = dicttoolz.itemfilter(lambda kv: _keep(kv, check_proj), item.assets)
+
+        if len(data_bands) == 0 and check_proj:
+            # If no data bands found with check_proj=True, fallback to check_proj=False
+            # This handles items that declare proj extension at item level but don't have
+            # per-asset proj data (shape/transform)
+            data_bands = dicttoolz.itemfilter(lambda kv: _keep(kv, False), item.assets)
 
         bands: dict[BandKey, RasterBandMetadata | AuxBandMetadata] = {}
         aliases = alias_map_from_eo(item)
@@ -665,6 +671,15 @@ def _bootstrap(self, item: pystac.item.Item) -> None:
         data_asset_names = set(n for n, _ in meta.bands if n in item.assets)
         data_assets = {n: item.assets[n] for n in data_asset_names}
 
+        # Check if any data assets have proj data.
+        # If item declares proj extension but assets don't have proj data, fall back to has_proj=False
+        if (
+            has_proj
+            and data_assets
+            and not any(has_proj_data(a) for a in data_assets.values())
+        ):
+            has_proj = False
+
         # We assume that grouping of data bands into grids is consistent across
         # entire collection, so we compute it once and keep it
         if has_proj:

tests/test_mdtools.py

@@ -298,6 +298,29 @@ def test_noassets_case(no_bands_stac) -> None:
     assert len(md.bands) == 0
 
 
+def test_partial_proj_fallback(partial_proj_stac: pystac.item.Item) -> None:
+    """
+    Test that items declaring proj extension but without per-asset proj data
+    fall back correctly and don't produce empty datasets.
+    Regression test for https://github.com/opendatacube/odc-stac/issues/251
+    """
+    # Item declares proj extension but assets don't have proj:shape/transform
+    item = partial_proj_stac
+    assert has_proj_ext(item) is True
+
+    # Extract collection metadata - should fall back to has_proj=False
+    md = extract_collection_metadata(item)
+    assert len(md.bands) > 0, "Should have found data bands with fallback"
+    assert md.has_proj is False, "Should have fallen back to has_proj=False"
+
+    # Parse item - should successfully extract bands
+    parsed = parse_item(item, md)
+    assert len(parsed.bands) == len(item.assets), "All assets should be parsed as bands"
+    # Verify bands are parsed correctly
+    for asset_name in item.assets:
+        assert (asset_name, 1) in parsed.bands, f"Asset {asset_name} should be in bands"
+
+
 def test_extract_md_raster_ext(
     sentinel_stac_ms_with_raster_ext: pystac.item.Item,
 ) -> None: