Tune segmentation: reduce over-splitting and clean polygon shapes

- Fusion: raise split threshold from 15% to 30% of plane (RADIO roof
prompts are too similar to split on small differences)
- Fusion: raise min component size from 200 to 500 px, fraction from
10% to 20% of plane
- Merge: raise small fragment threshold from 3% to 5% of building area
- GeoJSON: increase Douglas-Peucker epsilon from 1% to 2.5% of perimeter
for cleaner 4-6 vertex polygons instead of jagged 10-16

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

fusion.py

@@ -66,11 +66,13 @@ def fuse_segmentations(
                 continue
 
             fraction = count / plane_pixels
-            if fraction < 0.15:
-                # Too small to be a real sub-division
+            if fraction < 0.30:
+                # Must represent >30% of the plane to justify a split.
+                # The RADIO roof-type prompts are similar ("flat/pitched/hip/gable
+                # roof plane"), so smaller fractions are noise, not real sub-features.
                 continue
 
-            # This class represents >15% of the plane — check spatial coherence
+            # This class represents >30% of the plane — check spatial coherence
             sub_mask = plane_mask & (radio_roof_class == cls)
             labeled_sub, n_components = label(sub_mask)
 
@@ -79,7 +81,7 @@ def fuse_segmentations(
                 comp_size = comp_mask.sum()
 
                 # Only split if the sub-region is spatially coherent and large enough
-                if comp_size > plane_pixels * 0.1 and comp_size > 200:
+                if comp_size > plane_pixels * 0.20 and comp_size > 500:
                     fused[comp_mask] = next_id
                     next_id += 1
 
@@ -108,7 +110,7 @@ def split_disconnected_regions(label_map: np.ndarray) -> np.ndarray:
 def merge_small_fragments(
     label_map: np.ndarray,
     building_mask: np.ndarray,
-    min_fraction: float = 0.03,
+    min_fraction: float = 0.05,
 ) -> np.ndarray:
     """Merge fragments smaller than min_fraction of building area.
 

geo_export.py

@@ -101,9 +101,9 @@ def labels_to_geojson(
             if area_sqft < min_area_sqft:
                 continue
 
-            # Simplify polygon (1% of perimeter)
+            # Simplify polygon (2.5% of perimeter — clean roof plane shapes)
             perimeter = cv2.arcLength(contour, True)
-            epsilon = 0.01 * perimeter
+            epsilon = 0.025 * perimeter
             simplified = cv2.approxPolyDP(contour, epsilon, True)
 
             coords = [pixel_to_geo(pt[0][0], pt[0][1], w, h, bounds) for pt in simplified]

pipeline.py

@@ -158,7 +158,7 @@ def run(
     result.status.append("Fusing geometry + appearance...")
     fused = fuse_segmentations(ransac_labels, score_map, cropped_mask)
     fused = split_disconnected_regions(fused)
-    fused = merge_small_fragments(fused, cropped_mask, min_fraction=0.03)
+    fused = merge_small_fragments(fused, cropped_mask, min_fraction=0.05)
     result.fused_labels = fused
 
     n_final = len(set(np.unique(fused)) - {0})