Wasn't it LEO_BOLOGNA who wrote:
>My question is: in povray does splines (linear,quadratic or cubic) permit to
>define only curves or surface also?
>
>and, if it's possible to use splines to define a surface, does its degree
>have to be the same in "u" and "v" directions? or, for example, can I
>define a spline surface that has degree 1 in one direction and degree 2 in
>the other one?!?!

Spline functions themselves are always curves, not surfaces.

You can use splines in an isosurface function to draw surfaces that are
controlled by spline functions. You could use splines of different types
to control the x and z coordinates. In the third example on this page I
could just as well have used the x values from one spline and the z
values from a spline of a different type.

http://www.econym.demon.co.uk/isotut/more.htm

-- 
Mike Williams
Gentleman of Leisure

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