Am 03.05.2016 um 02:34 schrieb Bald Eagle:

> Oh, see - what I was thinking was that the WHOLE curve would be processed in
> context, which would not lead to your second scenario, but to:
> 
>>     A    B
>>   + |\  /|
>>   __| \/ |_____axis
> 
> Which ought to give the same as your first scenario, no?

That may be what you were thinking, but it's not what happens. It's
simply not how POV-Ray works internally.

It's not like POV-Ray iterates over all the points on an object's
surface and shoves each into the image, so that it could just shuffle
around points arbitrarily in 3D space as it goes along.

What POV-Ray instead does is that it iterates over all the points in the
result image, computes the line in 3D space that is projected onto that
point in the image, and then essentially solves a mathematical equation
to figure out all the points at which that line intersects any given
object in the scene.

Now if POV-Ray finds a point on a lathe, it is too late to do any
rotation by 180 degrees -- because the resulting point will most likely
not be on the line anymore.

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