"Andrew Cocker" <mai### [at] mariner9net> wrote in message
news:3d37da15@news.povray.org...
>
> Dammit, just spent all night rendering this, and you beat me to it :-)
>
> Actually, you will be the man to ask. In my (albeit) short experiment, I
> couldn't work out how to keep the strip closed. In this anim, Nr goes from
0
> to 4 (equalling 4*180 = 360 degrees. Correct?), and SA from 0 to 360.
Still,
> they twist at different speeds. Are they additive? ie does one act on the
> other, so they'll never be in sync? (I glanced at mobius.inc, got a
headache
> immediately, and thought better of it. Looks complicated!)
>

Very nice, I see you even tried the uv mapping.
As for your question: The strip is only closed when Nr is an integer (i.e. a
full half-twist) anything in between will only have partial twists and will
end up not being closed as such.  SA just defines the twist angle that the
mobius starts at (the start position is at the +x axis and runs ccw around
the y-axis).  Increasing SA from 0 to 360 will have the effect of the whole
mobius twisting around the NA, but won't add to the number of twists.
Increasing Nr from 0 to 4 will  (BTW 4*180 = 720!) cause more twists to be
added to the mobius, but as it increases between full twists, it will not be
closed.  There is no way to get from 0 twists to one complete 180 twist
smoothly without this happening.

-tgq

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