Am 09.05.2017 um 14:14 schrieb William F Pokorny:

> The great news is Christoph fixed ALL the sphere_sweep auto-bounding
> issues I have in hand in beta 6! The auto-bounding issue has dogged
> sphere_sweeps from day one with this object.

In a certain sense I cheated: Rather than trying to come up with a
formula to compute the minimum and maximum coordinates of a sphere sweep
based on a Catmull-Rom spline (the thing POV-Ray calls `cubic_spline`),
I just searched the Internerds for a formula to translate a Catmull-Rom
spline into a (temporary) equivalent Bezier spline, and then exploiting
the neat property that a Bezier spline can never "overshoot" its control
points.

There are cases where this approach gives a non-ideal (i.e. oversized)
bounding box, but that's acceptable, and the upside is that it'll never
give a bad (i.e. undersized) one.

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