Objects of this type (select object type Interface curved II) are very similar to user-defined interfaces on a rectangular basis that were discussed before. The difference is the shape of the basis which is a circle instead of a rectangle. The dialog to set the objects' parameters is this:

Location defines the center of the circle over which the surface profile is computed. Normal Vector is the surface normal, and Radius the radius of the circle.

The Function describes how the surface profile, i.e. the height of the curce, depends on the distance from the center. This distance must be called 'R' in the formula. The example leads to the following surface:

Some test rays (air-glass interface) show the consequences:

As the following example shows, user-defined interfaces with circular basis can be combined with open cylinders to study various shapes of fiber heads:

The definition of that interface covering the user-defined surface is the same as explained for rectangles.