Why thank you both _indeed_ for your quick replies.  It is _gratifying_ to
be told that I'm posting in the wrong group.

Unfortunately however my question does relate to the povray source.

The object I want to render has is mathematically reasonable, just as any
other povray primiative is.  And povray does not appear to support it.  I
_need_ to create a new primitive.

My question is: how do I create a new primitive?  It will be a finite patch
primitive (like polygon, etc.).  I know how to determine where a point in 3D
space is on the surface.  But I am not sure about how to calculate
intersections with rays, yet.

Given four points in space, A,B,C, and D, with line segments AB, and CD.
The surface is the set of all lines from each point on AB to its
corresponding point on CD.  (Corresponding means of the same ratio from the
ends of its line.)

I am assured that this is mathemetically well-defined.

Thanks,
Edmund.

"Edmund Horner" <ejr### [at] paradisenetnz> wrote in message
news:39ed4dbe@news.povray.org...
> I am considering how to render the shape of a "twisted square".
>
> The shape is defined by four points, with a surface made of straight lines
> forming a grid over the "square".  Apparently this is a quite reasonable
> shape, and is useful for making surfaces.
>
> But I do not think pov-ray provides it.  Anyone got any advice on how I
best
> go about adding it?
>
> Edmund.
>
>

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