Figure 9. Constraints imposed on smooth meshes in our optimization procedure. Left: For purposes of approximation, vertices vi of the mesh are kept close to the reference surface Φ, by adding the constraint that vi lies in the tangent plane of Φ in the point v∗ which was closest to vi in the previous iteration of our optimization procedure. Right: The spherical polygon n1,..., n6 is star-shaped w.r.t. the center nv if all triangles nknk+1nv have the same orientation and it winds around nv exactly once.