Merge pull request #56 from carboncredits/rhm31-fast-geometry-expansion

Make geometry expansion faster for complex geometry

Author: patricoferris

methods/common/geometry.py

@@ -13,15 +13,27 @@ def utm_for_geometry(lat: float, lng: float) -> int:
         epsg_code = 32600 + utm_band
     return epsg_code
 
+def expand_recurse_geoms(shape: shapely.Geometry, radius: float) -> shapely.Geometry:
+    # Calling .buffer directly on a shape is incredibly slow when it contains lots of geometry.
+    # So we call it on each piece of geometry instead. No reason that should be faster, but it is
+    if hasattr(shape, 'geoms'):
+        expanded = shapely.GeometryCollection([])
+        for geom in shape.geoms:
+            expand_geom = expand_recurse_geoms(geom, radius)
+            expanded = expanded.union(expand_geom)
+        return expanded
+    else:
+        return shape.buffer(radius)
+
 def expand_boundaries(source: gpd.GeoDataFrame, radius: float) -> gpd.GeoDataFrame:
     original_projection = source.crs
 
     utm_codes = np.array([utm_for_geometry(x.centroid.y, x.centroid.x) for x in source.geometry])
     utm_code = scipy.stats.mode(utm_codes, keepdims=False).mode
     projected_boundaries = source.to_crs(f"EPSG:{utm_code}")
 
-    expanded = [x.buffer(radius) for x in projected_boundaries.geometry]
-    simplified = shapely.unary_union(expanded)
+    project = projected_boundaries.unary_union
+    simplified = expand_recurse_geoms(project, radius)
 
     finished = gpd.GeoSeries(simplified)
     utm_result = gpd.GeoDataFrame.from_features(finished, crs=f"EPSG:{utm_code}")