Pointmap: replace slow poisson-disk sphere sampling with instant Fibonacci sphere

app.py

@@ -144,13 +144,25 @@ def _foreground_mask(image_pil: Image.Image, target_h: int, target_w: int) -> np
 # -----------------------------------------------------------------------------
 # Point cloud export
 
-def _camera_marker(radius: float = 0.04, n_points: int = 600,
+def _camera_marker(radius: float = 0.04, n_points: int = 800,
                    color=(0.20, 0.55, 0.96)) -> o3d.geometry.PointCloud:
-    """Small uniformly-blue sphere at the world origin marking the camera."""
-    sphere = o3d.geometry.TriangleMesh.create_sphere(radius=radius, resolution=24)
-    sphere.translate((0.0, 0.0, 0.0))
-    pc = sphere.sample_points_poisson_disk(number_of_points=n_points)
-    pc.colors = o3d.utility.Vector3dVector(np.tile(color, (len(pc.points), 1)))
+    """Small uniformly-blue sphere at the world origin marking the camera.
+
+    Manual Fibonacci-sphere sampling — instant, vs Open3D's poisson-disk which
+    can take seconds per call.
+    """
+    rng = np.random.default_rng(0)
+    i = np.arange(n_points)
+    phi = np.arccos(1 - 2 * (i + 0.5) / n_points)             # latitude
+    theta = np.pi * (1 + 5 ** 0.5) * (i + 0.5)                # golden-angle longitude
+    pts = np.stack([
+        radius * np.sin(phi) * np.cos(theta),
+        radius * np.sin(phi) * np.sin(theta),
+        radius * np.cos(phi),
+    ], axis=1)
+    pc = o3d.geometry.PointCloud()
+    pc.points = o3d.utility.Vector3dVector(pts.astype(np.float64))
+    pc.colors = o3d.utility.Vector3dVector(np.tile(color, (n_points, 1)).astype(np.float64))
     return pc