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

The CurveVectors class lets you generate different types of vectors
associated with a curve.  Arrows will be generated at the endpoint of
each subdivision of the curve (determined by the Domain directive).
The types of arrows are listed in the VECTOR menu, and you may select
as many as you want.  After selecting the vectors, press UPDATE to
compute them.  The VECTOR/UNIT menu means that the vectors will be
normalized to unit length.

The types of vetors are:

	Tangent		The unit tangent vector
	Normal		The unit normal vector
	Binormal	The unit binormal vector
	Velocity	The first derivative vector
	Acceleration	The second derivative vector 
	Surface Normal	For a CurveOnSurface, the normal to the
			  surface at the given point on the curve
	Surface Fu	For a CurveOnSurface, the first partial
			  derivative vector for the surface
	Surface Fv	For a CurveOnSurface, the second partial
			  derivative vector for the surface


The CurveVectors class supports all the standard directives, together
with the ArrowHead, ArrowScale and ArrowMaxLen directives of the Arrow
class, and the Domain directive of the CurveFromCurve class.