By envelope, you likely mean the convex hull. By "crosses inside the envelope", you probably mean it intersects the hull. That does not work. If you have a tria

By envelope, you likely mean the convex hull. By "crosses inside the envelope", you probably mean it intersects the hull. That does not work. If you have a triangle inside a triangle and a central point inside that, that gives you seven points. If you start on the inner triangle, intersecting the outer triangle (convex hull), you can repeatedly visit the points of the triangles without touching the central point.