Rune wrote in message <3c6d8a2c@news.povray.org>...
>I'm getting confused by cubic splines.
>
>Doesn't cubic splines work that way that any point on the spline is
>dependent on exactly four control points, no more, no less? At least that's
>the impression I get from the POV-Ray documentation, and when using cubic
>splines in prisms it works exactly that way indeed.
>
>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).

I tried using the four control point method for pure splines, but that
resulted in sharp turns at the control points.  The "all control points"
method gives a spline that is smooth along its entire length (essential for
those applications that require computing the second derivative of the
spline).

--
Mark

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