keep only a single dangle in a loop (#140)

Author: martinfleis

core/algorithms/simplify.py

@@ -346,57 +346,43 @@ def loop(
     )
     split_points.extend(splitters)
 
-    possible_dangle = possible_dangle[shapely.disjoint(possible_dangle, dropped)]
-    n_comps = graph.Graph.build_contiguity(
-        gpd.GeoSeries(possible_dangle), rook=False
-    ).n_components
-    if n_comps == 1:
-        logger.debug("LOOP components 1")
-        dangle_coins = momepy.COINS(
-            gpd.GeoSeries(shapely.line_merge(possible_dangle)).explode(),
-            flow_mode=True,
-        ).stroke_gdf()
-        candidate = dangle_coins.loc[dangle_coins.length.idxmax()].geometry
-        if candidate.intersects(snap_to.union_all().buffer(eps)) and (
-            candidate.length > min_dangle_length
-        ):
-            logger.debug("LOOP intersects and length > min_dangle_length")
-            if not primes.empty:
-                points = [
-                    shapely.get_point(candidate, 0),
-                    shapely.get_point(candidate, -1),
-                ]
-                distances = shapely.distance(points, highest_hierarchy.union_all())
-                if distances.max() > min_dangle_length:
-                    logger.debug("LOOP prime check passed")
-                    to_add.append(candidate)
-            else:
-                to_add.append(candidate)
-    elif n_comps > 1:
+    possible_dangle = gpd.GeoDataFrame(
+        geometry=possible_dangle[shapely.disjoint(possible_dangle, dropped)]
+    )
+    comps = graph.Graph.build_contiguity(
+        possible_dangle.difference(snap_to.union_all().buffer(eps)), rook=False
+    )
+    if comps.n_components > 1:
         # NOTE: it is unclear to me what exactly should happen here. I believe that
         # there will be cases when we may want to keep multiple dangles. Now keeping
         # only one.
         logger.debug("LOOP components many")
-        dangle_coins = momepy.COINS(
-            gpd.GeoSeries(shapely.line_merge(possible_dangle)).explode(),
-            flow_mode=True,
-        ).stroke_gdf()
-        candidate = dangle_coins.loc[dangle_coins.length.idxmax()].geometry
-        if candidate.intersects(snap_to.union_all().buffer(eps)) and (
-            candidate.length > min_dangle_length
-        ):
-            logger.debug("LOOP intersects and length > min_dangle_length")
-            if not primes.empty:
-                points = [
-                    shapely.get_point(candidate, 0),
-                    shapely.get_point(candidate, -1),
-                ]
-                distances = shapely.distance(points, highest_hierarchy.union_all())
-                if distances.max() > min_dangle_length:
-                    logger.debug("LOOP prime check passed")
-                    to_add.append(candidate)
-            else:
+        comp_labels = comps.component_labels.values
+        longest_component = possible_dangle.dissolve(
+            comps.component_labels
+        ).length.idxmax()
+        possible_dangle = possible_dangle[comp_labels == longest_component]
+
+    dangle_coins = momepy.COINS(
+        possible_dangle,
+        flow_mode=True,
+    ).stroke_gdf()
+    candidate = dangle_coins.loc[dangle_coins.length.idxmax()].geometry
+    if candidate.intersects(snap_to.union_all().buffer(eps)) and (
+        candidate.length > min_dangle_length
+    ):
+        logger.debug("LOOP intersects and length > min_dangle_length")
+        if not primes.empty:
+            points = [
+                shapely.get_point(candidate, 0),
+                shapely.get_point(candidate, -1),
+            ]
+            distances = shapely.distance(points, highest_hierarchy.union_all())
+            if distances.max() > min_dangle_length:
+                logger.debug("LOOP prime check passed")
                 to_add.append(candidate)
+        else:
+            to_add.append(candidate)
 
     return to_add