fix: Fix Polygon Repair and Empty Polygon Issues, see #1118

sahi/postprocess/utils.py

@@ -4,6 +4,7 @@
 import numpy as np
 import torch
 from shapely.geometry import MultiPolygon, Polygon
+from shapely.geometry.collection import GeometryCollection
 
 from sahi.annotation import BoundingBox, Category, Mask
 from sahi.prediction import ObjectPrediction
@@ -65,6 +66,71 @@ def tolist(self):
             return self.list
 
 
+def repair_polygon(shapely_polygon: Polygon) -> Polygon:
+    """
+    Fix polygons
+    :param shapely_polygon: Shapely polygon object
+    :return:
+    """
+    if not shapely_polygon.is_valid:
+        fixed_polygon = shapely_polygon.buffer(0)
+        if fixed_polygon.is_valid:
+            if isinstance(fixed_polygon, Polygon):
+                return fixed_polygon
+            elif isinstance(fixed_polygon, MultiPolygon):
+                return max(fixed_polygon.geoms, key=lambda p: p.area)
+            elif isinstance(fixed_polygon, GeometryCollection):
+                polygons = [geom for geom in fixed_polygon.geoms if isinstance(geom, Polygon)]
+                return max(polygons, key=lambda p: p.area) if polygons else shapely_polygon
+
+    return shapely_polygon
+
+
+def repair_multipolygon(shapely_multipolygon: MultiPolygon) -> MultiPolygon:
+    """
+    Fix invalid MultiPolygon objects
+    :param shapely_multipolygon: Imported shapely MultiPolygon object
+    :return:
+    """
+    if not shapely_multipolygon.is_valid:
+        fixed_geometry = shapely_multipolygon.buffer(0)
+
+        if fixed_geometry.is_valid:
+            if isinstance(fixed_geometry, MultiPolygon):
+                return fixed_geometry
+            elif isinstance(fixed_geometry, Polygon):
+                return MultiPolygon([fixed_geometry])
+            elif isinstance(fixed_geometry, GeometryCollection):
+                polygons = [geom for geom in fixed_geometry.geoms if isinstance(geom, Polygon)]
+                return MultiPolygon(polygons) if polygons else shapely_multipolygon
+
+    return shapely_multipolygon
+
+
+def coco_segmentation_to_shapely(segmentation: Union[List, List[List]]):
+    """
+    Fix segment data in COCO format
+    :param segmentation: segment data in COCO format
+    :return:
+    """
+    if isinstance(segmentation, List) and all([not isinstance(seg, List) for seg in segmentation]):
+        segmentation = [segmentation]
+    elif isinstance(segmentation, List) and all([isinstance(seg, List) for seg in segmentation]):
+        pass
+    else:
+        raise ValueError("segmentation must be List or List[List]")
+
+    polygon_list = []
+
+    for coco_polygon in segmentation:
+        point_list = list(zip(coco_polygon[::2], coco_polygon[1::2]))
+        shapely_polygon = Polygon(point_list)
+        polygon_list.append(repair_polygon(shapely_polygon))
+
+    shapely_multipolygon = repair_multipolygon(MultiPolygon(polygon_list))
+    return shapely_multipolygon
+
+
 def object_prediction_list_to_torch(object_prediction_list: ObjectPredictionList) -> torch.tensor:
     """
     Returns:
@@ -166,6 +232,12 @@ def get_merged_mask(pred1: ObjectPrediction, pred2: ObjectPrediction) -> Mask:
     # buffer(0) is a quickhack to fix invalid polygons most of the time
     poly1 = get_shapely_multipolygon(mask1.segmentation).buffer(0)
     poly2 = get_shapely_multipolygon(mask2.segmentation).buffer(0)
+
+    if poly1.is_empty:
+        poly1 = coco_segmentation_to_shapely(mask1.segmentation)
+    if poly2.is_empty:
+        poly2 = coco_segmentation_to_shapely(mask2.segmentation)
+
     union_poly = poly1.union(poly2)
     if not hasattr(union_poly, "geoms"):
         union_poly = MultiPolygon([union_poly])