KnotPlot (http://www.pims.math.ca/knotplot/) exports to POVRay in 
bicubic patches, but I'd never bothered to look at the actual code very 
closely.  It's surprisingly (well, I was surprised!) easy to extract the 
splines from the patches.  In this example, I set the number of patches 
around the "tube" to 3 (in the misc. panel of KnotPlot), so then if you 
strip off the first vector from each patch (which I did with a judicious 
use of "replace" in Microsoft Word, since I'm a total dunce at 
programming), you can make an array that has the 3 edge splines listed 
in order (0 .. Tot/3 - 1, Tot/3 .. 2*Tot/3 - 1, 2*Tot/3, Tot - 1, where 
Tot is the size of the array.)  I originally did this to check out Mike 
Williams' Rope macro, but I haven't gotten that far yet.  Anyway, if you 
use the 3 edge splines, you can make a center spline by averaging the 
edge ones.  Then, the sky's the limit.

Scene file available upon request.

Dave Matthews

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