Actually there are two things wrong with this
1. I accidently made the number of rails coincide with the number of frames,
so you don't get the feel of the rails moving, easy to fix
2. As for the back and forth motion, this comes from the camera speeding up
and slowing down.  When calculating the position on the ellipse, arc lengths
are a real mess to work with so I only used an approximation, the downfall
of which is that the distances calculated at the major axes of the ellipse
are closer together than those at the minor axes, the more eccentric the
ellipse is, the greater the difference of these distances.  When you make
the animation, the camera essentially gets sped up and down.  Very tough to
fix accurately without some complex maths (I will probably try to find a way
to fix it or better approximate it).  If I use a perfect circle, however,
this will disappear.

-tgq

"Lothar Esser" <les### [at] helixnihgov> wrote in message
news:3BB60306.5518CF15@helix.nih.gov...
> Very nice, I could watch this for hours !
>
> If you want to redo it as you indicated I have one comment:
> When I watch the rail, I get the impression that I slowly rock back and
forth. Maybe I have not
> been often enough on a roller coaster but there is something odd about the
movement
> of the observer. Unfortunately I cannot make good suggestions as to how to
improve it. It
> just might be an inevitable artifact of animation.
>
> Good work all in all.
>
> Lothar
>
>
>

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