Merge pull request #79 from zenWai/fix-regions-2d-heatmap

Resolve polygon overlay issues 2D

brainglobe_heatmap/heatmaps.py

@@ -1,4 +1,4 @@
-from typing import Dict, Optional, Tuple, Union
+from typing import Dict, List, Optional, Tuple, Union
 
 import matplotlib as mpl
 import matplotlib.pyplot as plt
@@ -353,13 +353,38 @@ def plot_subplot(
             self.regions_meshes, self.scene.root
         )
 
+        segments: List[Dict[str, Union[str, np.ndarray, float]]] = []
         for r, coords in projected.items():
-            name, segment = r.split("_segment_")
+            name, segment_nr = r.split("_segment_")
+            x = coords[:, 0]
+            y = coords[:, 1]
+            # calculate area of polygon with Shoelace formula
+            area = 0.5 * np.abs(
+                np.dot(x, np.roll(y, 1)) - np.dot(y, np.roll(x, 1))
+            )
+
+            segments.append(
+                {
+                    "name": name,
+                    "segment_nr": segment_nr,
+                    "coords": coords,
+                    "area": area,
+                }
+            )
+
+        # Sort region segments by area (largest first)
+        segments.sort(key=lambda s: s["area"], reverse=True)
+
+        for segment in segments:
+            name = segment["name"]
+            segment_nr = segment["segment_nr"]
+            coords = segment["coords"]
+
             ax.fill(
                 coords[:, 0],
                 coords[:, 1],
                 color=self.colors[name],
-                label=name if segment == "0" and name != "root" else None,
+                label=name if segment_nr == "0" and name != "root" else None,
                 lw=1,
                 ec="k",
                 zorder=-1 if name == "root" else None,