Add GLCM texture metrics to focal module (#963)

New xrspatial.glcm module with glcm_texture() for computing Haralick
texture features (contrast, dissimilarity, homogeneity, energy,
correlation, entropy) over a sliding window.

Supports numpy, dask+numpy, cupy, and dask+cupy backends. Dask path
pre-quantizes globally for consistent gray-level mapping across chunks.

Author: brendancol

xrspatial/__init__.py

@@ -44,6 +44,7 @@
 from xrspatial.flow_length import flow_length  # noqa
 from xrspatial.flow_path import flow_path  # noqa
 from xrspatial.focal import mean  # noqa
+from xrspatial.glcm import glcm_texture  # noqa
 from xrspatial.morphology import morph_closing  # noqa
 from xrspatial.morphology import morph_dilate  # noqa
 from xrspatial.morphology import morph_erode  # noqa

xrspatial/accessor.py

@@ -181,6 +181,10 @@ def focal_mean(self, **kwargs):
         from .focal import mean
         return mean(self._obj, **kwargs)
 
+    def glcm_texture(self, **kwargs):
+        from .glcm import glcm_texture
+        return glcm_texture(self._obj, **kwargs)
+
     # ---- Morphological ----
 
     def morph_erode(self, **kwargs):
@@ -545,6 +549,10 @@ def focal_mean(self, **kwargs):
         from .focal import mean
         return mean(self._obj, **kwargs)
 
+    def glcm_texture(self, **kwargs):
+        from .glcm import glcm_texture
+        return glcm_texture(self._obj, **kwargs)
+
     # ---- Morphological ----
 
     def morph_erode(self, **kwargs):