CenterStage Object Class:  CurveFromCurve
Subclass of:  Curve
Requires reference to a Curve object

The CurveFromCurve class lets you create a Curve object that relates to
another curve object.  The reference curve value is computed and is
used as the origin for the referring object at each value of the
parameter.  The CurveFromCurve's function is computed and the result
is added to the original curve's value, either in absolute
coordinates, or in relation to the curve's Frenet frame.

In addition to the standard Curve directives, CurveFromCurve supports
the following:

   Function param func [-frame | -absolute | -sframe]

	Here the "param" and "func" arguments are the same as for the
	standard Curve.  The -frame, -sframe and -absolute options
	determine whether the result of the function is in the coordinate
	system of the Frenet frame for the linked curve, the surface frame
	for the linked curve (if it is a CurveOnSurface object) or in
	absolute coordinates (the default).  If -frame or -sframe is
	specified, then both curves must be in 3-space, and the frame is
	computed numerically.  For -frame, the x, y and z coordinates
	correspond to the tangent, normal and binormal directions; for
	-sframe, the x, y and z coordinates correspond to the surface
	normal and the parametric directions with respect to the first
	and second variables for the curve's linked surface.

	For example:

		Function {t} {
		  let (T,N,B) = (0,d,0)
		} -frame

		Axes {T N B}

		Slider d 0 2

	produces a curve that is the offset curve to the original
	along the normal direction.  The offset distance is given by a
	slider, so a family of offset curves can be investigated.

	If the linked object is a CurveOnSurface, then

		Function {t} {
		  let (N,U,V) = (d,0,0)
		} -sframe

		Axes {N U V}

		Slider d 0 2

	produces a curve that is the offset curve to the original
	along the direction normal to the surface on which the curve lies
	(which is not usually the same as the binormal vector for the curve
	itself).

    Domain {Inherit}
	
	This special form of the domain command can be used to inherit
	the domain from the original curve.  Standard Domain
	specifications can also be used to provide a domain other than
	the one of the original curve.
