The window "Surface: X(u, v)" shows the hyperbolic paraboloid X(u, v) = (u, v, u

The window "Normal Image" shows the surface produced by mapping each point on the surface X(u,v) to its unit normal vector, preserving the coloring from the "Surface" window.

It is possible to change the point (u

In this demo, we indicate a surface and its tangent plane at p, and, in a separate window, the tangent plane at p viewed perpendicular to the unit normal vector at p. We may select a vector A in the tangent plane and the demonstration shows the image vector dn