bezier surface

Bezier surface

   <graphics> A surface defined by mathematical formulae, used in
   {computer graphics}.  A surface P(u, v), where u and v vary
   orthogonally from 0 to 1 from one edge of the surface to the
   other, is defined by a set of (n+1)*(m+1) "control points"
   (X(i, j), Y(i, j), Z(i, j)) for i = 0 to n, j = 0 to m.

   	P(u, v) = Sum i=0..n {Sum j=0..m [
   		(X(i, j), Y(i, j), Z(i, j))
   		* B(i, n, u) * B(j, m, v)]}

   	B(i, n, u) = C(n, i) * u^i * (1-u)^(n-i)

   	C(n, i) = n!/i!/(n-i)!

   Bezier surfaces are an extension of the idea of {Bezier
   curves}, and share many of their properties.

   (1996-06-12)