>
>> Couldn't you just "merge" the spheres and cylinders, then no cropping
>> should be necessary. A simple while or for loop in POV could create the
>> chain of spheres and cylinders, so long as your spheres are spaced close
>> enough it will look like a smooth curve. I did this a long time ago to
>> model speaker cable (two solid cores inside a semi-transparent case) and
>> it worked nicely.
>
> Ultimately I think this is what I should do.  Isosurfaces are a major
> performance increase over parametric surfaces, but the problem with using
> isosurfaces is the constraint equations become close to degenerate around the
> surface I'm trying to describe.  That, and I have to up the "accuracy" and
> "max_gradient" features so much that it starts to become slow again.
>
> I didn't know about the "while loop" feature in PoVRay until today.  That really
> helps!    I think this is the way to go.
>
>
>

I just tought of another possibility:
sor and lathe

You use the equation of the flat, 2D, hyperbola, evaluate it at many 
points using a #while loop.
Use those calculated points to define the curve. The sor and lathe will 
take care of makint it into a circular shape around the Y axis. You can 
translate and rotate the resulting object as you need.

If you add "open", there will be no end cap: You only get the actual 
surface with no thickness.

If you use an isosurface, "open" does the same.
Next, you can use some cylinder or cones to remove empty areas of the 
container box or sphere. It may help reduce the max_gradient. Use 
"evaluate" instead of max_gradient, it can make things somewhat faster.

Another option would be to subdivide your object using smaller 
containers, then, you recombine the parts with an union. Using boxes 
should be more effecient than spheres. That way, you may be able to work 
around the areas with the larger gradients.


Alain

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