Add edge detection filters (Sobel, Laplacian, Prewitt) (#1042)

* Add edge detection filters: Sobel, Laplacian, Prewitt (#1038)

Five new functions (sobel_x, sobel_y, laplacian, prewitt_x, prewitt_y)
that wrap convolution_2d with fixed 3x3 kernels. All four backends
(NumPy, CuPy, Dask+NumPy, Dask+CuPy) are inherited from the existing
convolution infrastructure.

* Add tests for edge detection filters (#1038)

72 tests covering correctness, NaN handling, edge cases, boundary modes,
and cross-backend (NumPy, Dask, CuPy) equivalence.

* Add edge detection filters to focal docs (#1038)

* Add edge detection user guide notebook (#1038)

Covers sobel_x, sobel_y, laplacian, prewitt_x, prewitt_y with
synthetic terrain, directional gradients, edge magnitude, Sobel
vs Prewitt comparison, and boundary mode visualization.

* Add edge detection filters to README feature matrix (#1038)

* Add edge detection methods to .xrs accessor (#1038)

Registers sobel_x, sobel_y, laplacian, prewitt_x, prewitt_y on both
the DataArray and Dataset xrs accessors.

Author: brendancol

README.md

@@ -347,6 +347,11 @@ write_vrt('mosaic.vrt', ['tile1.tif', 'tile2.tif'])  # generate VRT
 | [Focal Statistics](xrspatial/focal.py) | Computes summary statistics over a sliding neighborhood window | Standard | ✅️ | ✅️ | ✅️ | ✅️ |
 | [Bilateral](xrspatial/bilateral.py) | Feature-preserving smoothing via bilateral filtering | Tomasi & Manduchi 1998 | ✅️ | ✅️ | ✅️ | ✅️ |
 | [GLCM Texture](xrspatial/glcm.py) | Computes Haralick GLCM texture features over a sliding window | Haralick et al. 1973 | ✅️ | ✅️ | 🔄 | 🔄 |
+| [Sobel X](xrspatial/edge_detection.py) | Horizontal gradient via Sobel operator (detects vertical edges) | Sobel & Feldman 1968 | ✅️ | ✅️ | ✅️ | ✅️ |
+| [Sobel Y](xrspatial/edge_detection.py) | Vertical gradient via Sobel operator (detects horizontal edges) | Sobel & Feldman 1968 | ✅️ | ✅️ | ✅️ | ✅️ |
+| [Laplacian](xrspatial/edge_detection.py) | Omnidirectional second-derivative edge detector | Standard | ✅️ | ✅️ | ✅️ | ✅️ |
+| [Prewitt X](xrspatial/edge_detection.py) | Horizontal gradient via Prewitt operator (detects vertical edges) | Prewitt 1970 | ✅️ | ✅️ | ✅️ | ✅️ |
+| [Prewitt Y](xrspatial/edge_detection.py) | Vertical gradient via Prewitt operator (detects horizontal edges) | Prewitt 1970 | ✅️ | ✅️ | ✅️ | ✅️ |
 
 -------
 

docs/source/reference/focal.rst

@@ -41,6 +41,18 @@ GLCM Texture
    xrspatial.glcm.glcm_texture
 
 
+Edge Detection
+==============
+.. autosummary::
+   :toctree: _autosummary
+
+   xrspatial.edge_detection.sobel_x
+   xrspatial.edge_detection.sobel_y
+   xrspatial.edge_detection.laplacian
+   xrspatial.edge_detection.prewitt_x
+   xrspatial.edge_detection.prewitt_y
+
+
 Focal Statistics
 ================
 .. autosummary::