lars petter wrote:

> Hello!
> 
> At school, we're developing a modelling tool that will generate shapes such
> as bezier curves, parabolas, ellipses and such in povray.
> 
> In the tool we have the parametrisised functions for all the shapes, so when
> it comes to the Pov-Ray script-generation, we're thinking about using the
> Parametric Object.
> 
> However, our shapes are supposed to have thickness and a height as well, and
> the Pov-Ray online documentation says; "The parametric object is not a solid
> object it is "hollow", like a thin shell."
> 
> So then we're wondering if there is some way to make these objects have a
> thickness as well.. Like one does with the isosurfaces, just subtract the
> thickness from the equation or something...?
> 
> The perfect solution however, would be that something like this can be done:
> http://hovedprosjekter.hig.no/v2004/data/gruppe11/param_obj.gif
> 
> A rectangle is swept along a parametrisised 3d spline to construct the solid
> object.. is this possible?
> 
In a sense it can be done for bezier patches. If you have
a start bezier surface and a final bezier surface and move
the surface from initial to final position along a bezier
spline (possibly modulating by moving control points
each along different bezier splines) then the 'side-surface'
will be a set of bicubic patches again. (as you wil only
have the true positions in 3D space, you have to compute
the positions of the controlpoints 'backwards', but that
can be done).
So, yes, what the link shows can be done in POV (provided
the curve has a cubic equation.)

I would not be able to do an elepsis along a parabolic
path myself. I have not studied the required equations
in depth. ( I guess I would approximate the ellipses and
oparabolas with bezier splines and patches, but that
would be cheating ;) ).

   Andrel

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