Add nearest function to STRtree (issue #668) (#672)

* Update strtree.py

Add GEOSSTRtree_nearest_generic function from GEOS

* Update ctypes_declarations.py

Add GEOSSTRtree_nearest_generic function from GEOS

* Add files via upload

* Update test_strtree_nearest.py

shapely/ctypes_declarations.py

@@ -509,3 +509,10 @@ def prototype(lgeos, geos_version):
 
         lgeos.GEOSSTRtree_destroy.argtypes = [c_void_p]
         lgeos.GEOSSTRtree_destroy.restype = None
+
+    if geos_version >= (3, 6, 0):
+        lgeos.GEOSDistanceCallback = CFUNCTYPE(c_int, c_void_p, c_void_p, c_void_p, c_void_p)
+
+        lgeos.GEOSSTRtree_nearest_generic.argtypes = [
+            c_void_p, py_object, c_void_p, lgeos.GEOSDistanceCallback, py_object]
+        lgeos.GEOSSTRtree_nearest_generic.restype = c_void_p

shapely/strtree.py

@@ -61,6 +61,28 @@ def callback(item, userdata):
 
         return result
 
+    def nearest(self, geom):
+        if self._n_geoms == 0:
+            return None
+
+        envelope = geom.envelope
+
+        def callback(item1, item2, distance, userdata):
+            try:
+                geom1 = ctypes.cast(item1, ctypes.py_object).value
+                geom2 = ctypes.cast(item2, ctypes.py_object).value
+                dist = ctypes.cast(distance, ctypes.POINTER(ctypes.c_double))
+                lgeos.GEOSDistance(geom1._geom, geom2._geom, dist)
+                return 1
+            except:
+                return 0 
+
+        item = lgeos.GEOSSTRtree_nearest_generic(self._tree_handle, ctypes.py_object(geom), envelope._geom, \
+            lgeos.GEOSDistanceCallback(callback), None)
+        result = ctypes.cast(item, ctypes.py_object).value
+
+        return result
+
 if __name__ == "__main__":
     import doctest
     doctest.testmod()

tests/test_strtree_nearest.py

@@ -0,0 +1,27 @@
+from . import unittest
+
+from shapely.geometry import Point, Polygon
+from shapely.geos import geos_version
+from shapely.strtree import STRtree
+
+@unittest.skipIf(geos_version < (3, 6, 0), 'GEOS 3.6.0 required')
+class STRTreeNearest(unittest.TestCase):
+    def test_nearest(self):
+        tree = STRtree([
+            Polygon([(1,0),(2,0),(2,1),(1,1)]),
+            Polygon([(0,2),(1,2),(1,3),(0,3)]),
+            Point(0,0.5)])
+        result = tree.nearest(Point(0,0))
+        self.assertEqual(result, Point(0,0.5))
+        result = tree.nearest(Point(0,4))
+        self.assertEqual(result, Polygon([(0,2),(1,2),(1,3),(0,3)]))
+        result = tree.nearest(Polygon([(-0.5,-0.5),(0.5,-0.5),(0.5,0.5),(-0.5,0.5)]))
+        self.assertEqual(result, Point(0,0.5))
+
+
+def test_suite():
+    return unittest.TestLoader().loadTestsFromTestCase(STRTreeNearest)
+
+if __name__ == '__main__':
+    unittest.main()
+