Hughes, B. wrote:
>"LibraryMan" <mrm### [at] attnet> wrote in message
>news:web.3ed652f8a160507a738e706a0[at]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.
>

Thanks, I think I'm finally "on the right page" now.  I appreciate your
efforts!
--MMW

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