Example: Fillet Surface Data Format
You can find a fillet surface where a round or a fillet is placed on a curved edge, or on an edge with non-constant arc radii. On a straight edge, you would use a cylinder to represent the fillet. The following illustration shows a fillet surface.
Data format:
P(v) spline running along the u = 0 boundary
C(v) spline along the centers of the fillet arcs
T(v) spline of unit tangents to the axis of the fillet arcs
R(v) = P(v) - C(v)

(x,y,z) = C(v) + R(v) * cos(u) + T(v) X R(v) * sin(u)