refactor: reproject dtype and nodata handling

- allow dtype change as part of reprojection
- more consistent handling of destination fill
  value defaults between different implementations

odc/geo/_dask.py

@@ -9,19 +9,13 @@
 from ._blocks import BlockAssembler
 from .gcp import GCPGeoBox
 from .geobox import GeoBox, GeoboxTiles
-from .warp import Nodata, Resampling, _rio_reproject, resampling_s2rio
-
-
-def resolve_fill_value(dst_nodata, src_nodata, dtype):
-    dtype = np.dtype(dtype)
-
-    if dst_nodata is not None:
-        return dtype.type(dst_nodata)
-    if src_nodata is not None:
-        return dtype.type(src_nodata)
-    if np.issubdtype(dtype, np.floating):
-        return dtype.type("nan")
-    return dtype.type(0)
+from .warp import (
+    Nodata,
+    Resampling,
+    _rio_reproject,
+    resampling_s2rio,
+    resolve_fill_value,
+)
 
 
 def _do_chunked_reproject(
@@ -50,7 +44,11 @@ def _do_chunked_reproject(
         dtype = ba.dtype
 
     dst_shape = ba.with_yx(ba.shape, dst_gbox.shape)
-    dst = np.zeros(dst_shape, dtype=dtype)
+    dst = np.full(
+        dst_shape,
+        resolve_fill_value(dst_nodata, src_nodata, dtype),
+        dtype=dtype,
+    )
 
     for src_roi in ba.planes_yx():
         src = ba.extract(src_nodata, dtype=dtype, casting=casting, roi=src_roi)
@@ -79,6 +77,7 @@ def dask_rio_reproject(
     dst_nodata: Nodata = None,
     ydim: int = 0,
     chunks: Optional[Tuple[int, int]] = None,
+    dtype=None,
     **kwargs,
 ) -> da.Array:
     # pylint: disable=too-many-arguments, too-many-locals
@@ -92,6 +91,9 @@ def dask_rio_reproject(
     def with_yx(a, yx):
         return (*a[:ydim], *yx, *a[ydim + 2 :])
 
+    if dtype is None:
+        dtype = src.dtype
+
     name: str = kwargs.pop("name", "reproject")
 
     gbt_src = GeoboxTiles(s_gbox, src.chunks[ydim : ydim + 2])
@@ -100,6 +102,7 @@ def with_yx(a, yx):
 
     dst_shape = with_yx(src.shape, d_gbox.shape.yx)
     dst_chunks: Tuple[Tuple[int, ...], ...] = with_yx(src.chunks, gbt_dst.chunks)
+    fill_value = resolve_fill_value(dst_nodata, src_nodata, dtype)
 
     tk = uuid4().hex
     name = f"{name}-{tk}"
@@ -111,15 +114,14 @@ def with_yx(a, yx):
         gbt_src,
         gbt_dst,
         src_nodata=src_nodata,
-        dst_nodata=dst_nodata,
+        dst_nodata=fill_value,
         axis=ydim,
         resampling=resampling,
+        dtype=dtype,
         **kwargs,
     )
     src_block_keys = src.__dask_keys__()
 
-    fill_value = resolve_fill_value(dst_nodata, src_nodata, src.dtype)
-
     def _src(idx):
         a = src_block_keys
         for i in idx:
@@ -141,4 +143,4 @@ def _src(idx):
 
     dsk = HighLevelGraph.from_collections(name, dsk, dependencies=(src,))
 
-    return da.Array(dsk, name, chunks=dst_chunks, dtype=src.dtype, shape=dst_shape)
+    return da.Array(dsk, name, chunks=dst_chunks, dtype=dtype, shape=dst_shape)

odc/geo/_xr_interop.py

@@ -45,6 +45,7 @@
 from .overlap import compute_output_geobox
 from .roi import roi_is_empty
 from .types import Resolution, SomeResolution, SomeShape, xy_
+from .warp import resolve_fill_value
 
 # pylint: disable=import-outside-toplevel
 # pylint: disable=too-many-lines
@@ -63,6 +64,8 @@
 
 # these attributes are pruned during reproject
 SPATIAL_ATTRIBUTES = ("crs", "crs_wkt", "grid_mapping", "gcps", "epsg")
+NODATA_ATTRIBUTES = ("nodata", "_FillValue")
+REPROJECT_SKIP_ATTRS: set[str] = set(SPATIAL_ATTRIBUTES + NODATA_ATTRIBUTES)
 
 # dimensions with these names are considered spatial
 STANDARD_SPATIAL_DIMS = [
@@ -654,6 +657,7 @@ def xr_reproject(
     *,
     resampling: Union[str, int] = "nearest",
     dst_nodata: Optional[float] = None,
+    dtype=None,
     resolution: Union[SomeResolution, Literal["auto", "fit", "same"]] = "auto",
     shape: Union[SomeShape, int, None] = None,
     tight: bool = False,
@@ -728,10 +732,10 @@ def xr_reproject(
     }
     if isinstance(src, xarray.DataArray):
         return _xr_reproject_da(
-            src, how, resampling=resampling, dst_nodata=dst_nodata, **kw
+            src, how, resampling=resampling, dst_nodata=dst_nodata, dtype=dtype, **kw
         )
     return _xr_reproject_ds(
-        src, how, resampling=resampling, dst_nodata=dst_nodata, **kw
+        src, how, resampling=resampling, dst_nodata=dst_nodata, dtype=dtype, **kw
     )
 
 
@@ -750,6 +754,7 @@ def _xr_reproject_ds(
     *,
     resampling: Union[str, int] = "nearest",
     dst_nodata: Optional[float] = None,
+    dtype=None,
     **kw,
 ) -> xarray.Dataset:
     assert isinstance(src, xarray.Dataset)
@@ -776,7 +781,12 @@ def _maybe_reproject(dv: xarray.DataArray):
                 dv = dv.drop_vars(strip_coords)
             return dv
         return _xr_reproject_da(
-            dv, how=dst_geobox, resampling=resampling, dst_nodata=dst_nodata, **kw
+            dv,
+            how=dst_geobox,
+            resampling=resampling,
+            dst_nodata=dst_nodata,
+            dtype=dtype,
+            **kw,
         )
 
     return src.map(_maybe_reproject)
@@ -788,6 +798,7 @@ def _xr_reproject_da(
     *,
     resampling: Union[str, int] = "nearest",
     dst_nodata: Optional[float] = None,
+    dtype=None,
     **kw,
 ) -> xarray.DataArray:
     # pylint: disable=too-many-locals
@@ -809,6 +820,9 @@ def _xr_reproject_da(
     else:
         dst_geobox = src.odc.output_geobox(how, **kw_gbox)
 
+    if dtype is None:
+        dtype = src.dtype
+
     # compute destination shape by replacing spatial dimensions shape
     ydim = src.odc.ydim
     assert ydim + 1 == src.odc.xdim
@@ -817,8 +831,8 @@ def _xr_reproject_da(
     src_nodata = kw.pop("src_nodata", None)
     if src_nodata is None:
         src_nodata = src.odc.nodata
-    if dst_nodata is None:
-        dst_nodata = src_nodata
+
+    fill_value = resolve_fill_value(dst_nodata, src_nodata, dtype)
 
     if is_dask_collection(src):
         from ._dask import dask_rio_reproject
@@ -829,12 +843,13 @@ def _xr_reproject_da(
             dst_geobox,
             resampling=resampling,
             src_nodata=src_nodata,
-            dst_nodata=dst_nodata,
+            dst_nodata=fill_value,
             ydim=ydim,
+            dtype=dtype,
             **kw,
         )
     else:
-        dst = numpy.empty(dst_shape, dtype=src.dtype)
+        dst = numpy.full(dst_shape, fill_value, dtype=dtype)
 
         dst = rio_reproject(
             src.values,
@@ -843,17 +858,17 @@ def _xr_reproject_da(
             dst_geobox,
             resampling=resampling,
             src_nodata=src_nodata,
-            dst_nodata=dst_nodata,
+            dst_nodata=fill_value,
             ydim=ydim,
+            dtype=dtype,
             **kw,
         )
 
-    attrs = {k: v for k, v in src.attrs.items() if k not in SPATIAL_ATTRIBUTES}
-    if dst_nodata is None:
-        attrs.pop("nodata", None)
-        attrs.pop("_FillValue", None)
-    else:
-        attrs.update(nodata=maybe_int(dst_nodata, 1e-6))
+    attrs = {k: v for k, v in src.attrs.items() if k not in REPROJECT_SKIP_ATTRS}
+    if numpy.isfinite(fill_value) and (
+        dst_nodata is not None or src_nodata is not None
+    ):
+        attrs.update({k: maybe_int(float(fill_value), 1e-6) for k in NODATA_ATTRIBUTES})
 
     # new set of coords (replace x,y dims)
     # discard all coords that reference spatial dimensions

odc/geo/warp.py

@@ -17,6 +17,15 @@
 Nodata = Optional[Union[int, float]]
 _WRP_CRS = "epsg:3857"
 
+__all__ = [
+    "resampling_s2rio",
+    "is_resampling_nn",
+    "resolve_fill_value",
+    "warp_affine",
+    "warp_affine_rio",
+    "rio_reproject",
+]
+
 
 def resampling_s2rio(name: str) -> rasterio.warp.Resampling:
     """
@@ -38,6 +47,18 @@ def is_resampling_nn(resampling: Resampling) -> bool:
     return resampling == rasterio.warp.Resampling.nearest
 
 
+def resolve_fill_value(dst_nodata, src_nodata, dtype):
+    dtype = np.dtype(dtype)
+
+    if dst_nodata is not None:
+        return dtype.type(dst_nodata)
+    if np.issubdtype(dtype, np.floating):
+        return dtype.type("nan")
+    if src_nodata is not None:
+        return dtype.type(src_nodata)
+    return dtype.type(0)
+
+
 def warp_affine_rio(
     src: np.ndarray,
     dst: np.ndarray,
@@ -129,15 +150,14 @@ def rio_reproject(
     :returns: dst
     """
     assert src.ndim == dst.ndim
-    if dst_nodata is None:
-        if dst.dtype.kind == "f":
-            dst_nodata = np.nan
 
     if src.ndim == 2:
         return _rio_reproject(
             src, dst, s_gbox, d_gbox, resampling, src_nodata, dst_nodata, **kwargs
         )
 
+    fill_value = resolve_fill_value(dst_nodata, src_nodata, dst.dtype)
+
     if ydim is None:
         # Assume last two dimensions are Y/X
         ydim = src.ndim - 2
@@ -154,9 +174,9 @@ def rio_reproject(
             dst[roi],
             s_gbox,
             d_gbox,
-            resampling,
-            src_nodata,
-            dst_nodata,
+            resampling=resampling,
+            src_nodata=src_nodata,
+            dst_nodata=fill_value,
             **kwargs,
         )
     return dst

tests/test_xr_interop.py

@@ -425,6 +425,9 @@ def test_xr_reproject(xx_epsg4326: xr.DataArray):
     assert xx.odc.geobox == dst_gbox
     assert xx.encoding["grid_mapping"] == "spatial_ref"
     assert "crs" not in xx.attrs
+    assert xx.dtype == xx_epsg4326.dtype
+
+    assert xx_epsg4326.odc.reproject(3857, dtype="float32").dtype == "float32"
 
     yy = xr.Dataset({"a": xx0, "b": xx0 + 1, "c": xr.DataArray([2, 3, 4])})
     assert isinstance(yy.odc, ODCExtensionDs)