On 2020-05-04 3:56 AM (-4), William F Pokorny wrote:
> 
> FYI. I've not recently looked at it, but back in 2006 Bruno Cabasson 
> worked up some code for elliptical tori implemented with sphere_sweeps 
> and blobs. Perhaps useful to review that work as we look for an 
> f_elliptical_torus() or complete parametric solution.
> 
> Given we can use blobs as potential patterns in functions/isosurfaces in 
> v38, perhaps this a path to something practical for Cousin Ricky?
> 
> The sphere_sweep as a general solution is not very attractive in v37 and 
> prior due bugs. Situations is better in v38 - and still better in povr 
> but the sphere_sweep probably not the fastest.
> 
> With both approaches expect tolerances to any math ideal, but perhaps we 
> are stuck with a fuzzy result in any case?

Sphere sweeps are unsatisfactory.  The attachment shows that the inner 
and outer curves are not ellipses.  The discrepancy does decrease with 
the ratio of the minor radius to the major radii and the eccentricity of 
the shape, but I would prefer a mathematical match at all scales.

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