Pointmap: surfel size from bbox diag/sqrt(N) (proper 2D-surface formula); factor 1.5 for clear overlap

app.py

@@ -272,13 +272,15 @@ def _make_glb(image_pil_texture: Image.Image, pointmap_hwc: np.ndarray,
     centroid = pts.mean(axis=0).astype(np.float32) if len(pts) else np.zeros(3, np.float32)
     pts = pts - centroid
 
-    # Surfel size from KD-tree median nearest-neighbour distance.
-    # Factor 0.6 → adjacent surfels overlap slightly along the surface so
-    # there are no visible gaps between tiles.
+    # Surfel size: surface-spacing estimate = bbox diagonal / sqrt(N).
+    # This is geometrically correct for points distributed across a 2D surface;
+    # raw KD-tree NN distance is biased too small (adjacent pixels often map
+    # to nearly-coincident 3D points, pulling the median way below the actual
+    # visual spacing). Factor 1.5 gives clear overlap so the surface reads
+    # as solid skin rather than a sparse tile pattern.
     if len(pts) >= 2:
-        from scipy.spatial import cKDTree
-        nn_dist = cKDTree(pts).query(pts, k=2)[0][:, 1]
-        r = max(float(np.median(nn_dist)) * 0.6, 1e-4)
+        extent_diag = float(np.linalg.norm(np.ptp(pts, axis=0)))
+        r = max(extent_diag / np.sqrt(len(pts)) * 1.5, 1e-4)
     else:
         r = 0.005