>But the cubic spline used in the spline feature in POV-Ray 3.5 works
>completely differently. It seems that there any point on the spline is
>dependent on all the control points, or at least much more than four as far
>as I can see. The code below illustrates it (POV-Ray 3.5 beta 11).

Well, I don't have a copy of Povray handy to fire up and play with,
but as I understand it, the spline of any *segment* depends on exactly
4 points.  But splines can have more than 1 segment.

So with the points 0-6 in your example, you'd have the following
segments:

Segment 0:  exists between points 1 and 2, defined by points 0, 1, 2, 3
Segment 1:  exists between points 2 and 3, defined by points 1, 2, 3, 4
        2:                        3     4                    2, 3, 4, 5
        3:                        4     5                    3, 4, 5, 6

Jamie

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