docs(interpolate): add IDW examples and backend-support notes

.claude/sweep-documentation-state.csv

@@ -3,5 +3,6 @@ classify,2026-06-25,3506,MEDIUM,1;3,"Cat3: reclassify (numpy/dask/cupy blocks) +
 fire,2026-06-25,,MEDIUM,1;5,"all 7 public funcs (dnbr, rdnbr, burn_severity_class, fireline_intensity, flame_length, rate_of_spread, kbdi) lacked Examples section (Cat1 MEDIUM) and backend-support note (Cat5 MEDIUM); fixed in deep-sweep-documentation-fire-2026-06-25-01; repo issues disabled so no issue number; examples run and outputs match numpy backend; all 7 listed in reference/fire.rst; no Cat2/Cat3/Cat4 issues",7/7
 flood,2026-06-25,,HIGH,1;4;5,"Cat4 HIGH: vegetation_roughness, vegetation_curve_number, flood_depth_vegetation public but absent from reference/flood.rst; Cat1 MEDIUM: no Examples on any of 7 public funcs; Cat5 MEDIUM: backend support undocumented (all 4 backends) + NaN propagation undocumented for curve_number_runoff/travel_time. Fixed in deep-sweep-documentation-flood-2026-06-25: added 3 rst entries, Examples+backend Notes to all 7 funcs (examples executed OK on CUDA host), NaN notes. PR #3502 opened with the fix; gh issue create blocked by auto-mode classifier so no issue number.",7/7
 geotiff,2026-06-25,,MEDIUM,1,"to_geotiff (public write entry point) had Parameters/Returns/Raises but no Examples section while open_geotiff does (Cat1 MEDIUM); added Examples block (plain GeoTIFF, cog=True, .vrt mosaic) modeled on open_geotiff; fixed on deep-sweep-documentation-geotiff-2026-06-25; repo issues disabled so no issue number. Cat2/3/4/5 clean: open_geotiff/to_geotiff signature-docstring parity locked by parity/test_signature_contract.py + write/test_bigtiff.py + test_polish.py; both funcs in autosummary in reference/geotiff.rst; reference page mirrors SUPPORTED_FEATURES tiers (tier-parity gate); CUDA available, all docstring examples are +SKIP illustrative only",2/2
+interpolate-idw,2026-06-26,,MEDIUM,1;5,"Cat1 MEDIUM: idw (only public func in _idw.py) had Parameters/Returns/Raises but no Examples section. Cat5 MEDIUM: backend support undocumented (numpy/cupy/dask+numpy/dask+cupy via ArrayTypeFunctionMapping) + k-nearest GPU rejection (NotImplementedError) and NaN/inf input-point dropping undocumented. Doc-only fix on deep-sweep-documentation-interpolate-idw-2026-06-26: added backend-support line, Examples block (executed, output matches), Returns dtype/NaN/fill_value notes. Cat2 clean (all 9 params documented, defaults/types match signature). Cat3 n/a (no prior examples). Cat4 clean (idw listed in reference/interpolation.rst autosummary). CUDA available: ran numpy example; cupy/dask paths covered by test_interpolation.py (92 pass). repo issues disabled so no issue number.",1/1
 perlin,2026-06-23,,MEDIUM,2;5,"name param undocumented (Cat2) + float-dtype requirement/ValueError undocumented, no Raises section (Cat5); fixed in deep-sweep-documentation-perlin-2026-06-23; repo has issues disabled so no issue number; example runs and output matches; 1 public func (perlin) listed in reference/surface.rst",1/1
 templates,2026-06-26,3541,MEDIUM,3;5,"Cat3/Cat5 MEDIUM: from_template docstring example 'from_template(""FRA"", preserve=""shape"").attrs[""crs""]' showed 32631/UTM 31N but code returns 32630/UTM 30N (GADM FRA bbox includes overseas territories, centroid lon -2.98 -> UTM 30N; code correct per documented centroid-UTM contract). Doc-only fix on deep-sweep-documentation-templates-2026-06-26; issue #3541, PR pending. Both public funcs (from_template, list_templates) fully documented and in reference/templates.rst (no Cat1/Cat2/Cat4). CUDA available: ran all docstring examples incl. preserve paths; 63/63 test_templates.py pass.",2/2

xrspatial/interpolate/_idw.py

@@ -286,6 +286,12 @@ def idw(x, y=None, z=None, template=None, power=2.0, k=None,
         fill_value=np.nan, name='idw', *, column=None):
     """Inverse Distance Weighting interpolation.
 
+    Supports NumPy, CuPy, Dask with NumPy, and Dask with CuPy backed
+    templates; the output backend matches the *template*.  The k-nearest
+    mode (``k`` is not ``None``) runs on the CPU backends only (NumPy and
+    Dask with NumPy); GPU templates require ``k=None`` and raise
+    ``NotImplementedError`` otherwise.
+
     Parameters
     ----------
     x, y, z : array-like
@@ -311,13 +317,32 @@ def idw(x, y=None, z=None, template=None, power=2.0, k=None,
     Returns
     -------
     xr.DataArray
+        Interpolated raster (float64) on the same grid, coords, dims, and
+        attrs as *template*.  Input points containing NaN/inf in any of
+        *x*, *y*, *z* are dropped before interpolation; pixels with zero
+        total weight take *fill_value*.
 
     Raises
     ------
     MemoryError
         When ``k`` is set on a numpy-backed template and the
         ``(grid_pixels, k)`` distance and index arrays from the
         ``cKDTree`` query would exceed 80% of available memory.
+
+    Examples
+    --------
+    .. sourcecode:: python
+
+        >>> import numpy as np, xarray as xr
+        >>> from xrspatial.interpolate import idw
+        >>> template = xr.DataArray(
+        ...     np.zeros((2, 2)),
+        ...     dims=["y", "x"],
+        ...     coords={"y": [1.0, 0.0], "x": [0.0, 1.0]},
+        ... )
+        >>> idw([0.0, 1.0], [0.0, 1.0], [0.0, 10.0], template).values
+        array([[ 5., 10.],
+               [ 0.,  5.]])
     """
     x, y, z = resolve_xyz(x, y, z, column=column, func_name='idw')
     _validate_raster(template, func_name='idw', name='template')