  The control polygon of a Bezier curve is well-defined and has geometric
significance---there is a sequence of weights under which the limiting position
of the curve is the control polygon. For a Bezier surface patch, there are many
possible polyhedral control structures, and none are canonical. We propose a
not necessarily polyhedral control structure for surface patches, regular
control surfaces, which are certain C^0 spline surfaces. While not unique,
regular control surfaces are exactly the possible limiting positions of a
Bezier patch when the weights are allowed to vary.
