If you look at the p.b.animation newsgroup, you can see my recent posts 
with my current project, which is a program that converts No Limits 
(http://www.nolimitscoaster.de - domain is .de, but the site is in 
English) roller coaster tracks into a POV-Ray scene.

My problem is figuring out banking.  No Limits uses bezier curves to 
define the track, and each point has a banking value.  The problem comes 
when you make a vertical loop.  At the entrance and exit of the loop, 
the banking is 0.  At the top, the banking is 180.

Because of this, I can't just use simple interpolation between banking 
angles.  Otherwise, the track twists 90 degrees as it enters and exits 
the loop.  This effect can be seen at 
http://www.sohcahtoa.net/images/thriller.png.

Another problem (which probably will have the same solution) is with 
corkscrew elements (A good example can be seen at 
http://www.rcdb.com/ig13.htm?picture=4).  If you defined a corkscrew 
with 5 points, the first point would have zero banking, then 90, 180, 
but the next to last ends up being either 270 or -90, and the last ends 
up being 0, but is guaranteed not to be 360.  The No Limits track editor 
won't allow it.  If you try to rotate it past 270, nothing happens.  It 
stays at 270.  But then if you put it to 0, it looks exactly as 
expected, and you get your nice smooth corkscrew.

Does anyone know how I could implement a system to calculate banking 
like this?

-DJ

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