No.. really. it's ok I got it :}   spline coordinates can be found in the *.ai files
that
adobe illustrator saves in.   I was just using Moray which doesn't support bezier
splines and
forgot that povray did.

David Wilkinson wrote:

> On Wed, 26 Jan 2000 23:56:25 -0700, Bret Slivka <coo### [at] chispnet> wrote:
>
> >Is there away to convert a bicubic, or bezier spline as used in
> >illustrator to a cubic spline as used in povray, to make smooth prism or
> >lathe objects with contours defined in illustrator-- or any other
> >program or spline designer?  I don't know the math behind a cubic spline
> >and have been unable to find it on the internet so far. I've noticed the
> >behavior of a cubic spline and noticed that it's difficult to make sharp
> >corners.. of course, unless you use multiple sections. The problem with
> >this is that multiple spline sections would produce a discontinuous
> >shape in povray... and I believe that the starting and ending points of
> >a prism object are required to be identical. I've resorted to simply
> >using a linear aproximation of the bezier spline in the prism which is
> >fairly satisfactory.. but it would be nice to know this for future
> >reference anyway.
>
> As Thomas Willhalm has already said, bi-cubics are used to define patches, not space
> curves, although the boundary curves of these patches are cubics.
> .
> It is quite easy to use Bezier splines to define smooth curves for use in POV lathe
or
> prism objects.  The bottle macro that I posted in povray.binaries.scene-files on 21
Dec 99
> uses Bezier splines to make the outline of the bottle.  This uses several spline
segments
> and as I wanted them to blend I ensured that the slopes at the common end point of
two
> connected splines were the same.  If I had wanted sharp corners I would have allowed
each
> curve to have different slopes at the common point. The real point of using spline
curves
> is that they can be used as piecewise curves to approximate to any sort of curve -
with or
> without slope discontinuities.
>
> Bezier splines can be used in a prism in exactly the same manner.  You can have a
series
> of segments and these can have straight lines, corners and curves. I give a simple
example
> below.
>
> I can appreciate your problems in trying to make the output of your spline generator
> programs relate to the POV spline, but there may be other spline generators that do
this.
> I suggest that you have a look through Ken Tyler's links at
http://www.povray.org/links/
>
> \\ ****** POV source starts.
> camera
> { location  <0, 1, -4.0>
>   direction 1.5*z
>   right     4/3*x
>   look_at   <1, 0.5,  0.0>}
> light_source { <-60, 60, -30> color rgb 1 }
> light_source { <60, 60, -30> color rgb 1 }
>
> // Prism constructed of bezier curves.
> // Note.  The second and third points in each bezier segment are control points.
> //        They do not necessarily lie on the curve, but are on the tangent to the
> //         curve at the adjacent point in that segment.  The length of this tangent
> //         affects the curvature of the curve.
>   prism {
>     bezier_spline
>     0,0.2, 28,
>     <0,0> <0.2,0.3> <0.4,0.6> <0.7,0.6>   // 1st segment
>     <0.7,0.6> <1.1,0.6> <1.1,1> <1.4, 1>
>     <1.4,1> <1.6,1> <1.8,1> <2,1>
>     <2,1> <2,0.6> <2,0.4> <2,0>
>     <2,0> <1.8,0> <1.6,0> <1.6,0>
>     <1.6,0> <1.6,0.5> <1.2,0> <0.8,0>
>     <0.8,0> <0.6,0> <0.2,0> <0,0>   // 7th segment
>     sturm   // this is usually necessary to ensure no glitches when rendering.
>     pigment { rgb <1,1,0>}
>     rotate -x*110
>   }
> //***** end of pov source.
>
> ----------------------------
> dav### [at] cwcomnet
> http://www.hamiltonite.mcmail.com
> ----------------------------

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