"LibraryMan" <mrm### [at] attnet> wrote in message
news:web.3ed652f8a160507a738e706a0@news.povray.org...
> ingo wrote:
> >
> >For a better understanding why more points are needed for a cubic spline
> >read section "6.5.1.7  Lathe" of the documention.
> >
> I *do* understand why control points are needed, but I'd expect they had
to
> be expressed as vectors.  The incremented float values in the example
don't
> seem to *be* expressing vectors, hence my confusion.  I thought vectors
had
> to be enclosed by '< >'.

Um, okay, here goes another of my explanations: Vectors ARE vectors  ;)
such as <1,2>, <1,2,3>, <1,2,3,4> and <1,2,3,4,5>; which are the possible
kind POV-Ray uses. Seems you have gotten lost about the meaning of that t
value used in splines. They are similar to the color_map index values that
are used to place a (color) vector, but in the case of spline you might
think of them as determining placement of the associated vectors as a
function of time or number sequence. In the spline, control points are both
float and vector together. Other things that use cubic_spline, like lathe,
aren't using a time or sequence float to space the points out. The lathe
gets its spacing from the y part of the vector, I guess that might be a good
way of saying it, since it typically is thought of as being drawn along the
y axis.

Bob H.

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