Check these weird images out: loop pic another loop pic Hi there. Ive been experimenting with creating a race track with the help of catmull-rom interpolation. For every small segment I calculate the tangent for it. Then I need the a right-vector to be able to construct the geometry. I get this by first taking the cross product of the tangent and [0 0 1] (to get the z-axis to be the up vector), then I rotate that vector by X degrees (every segment has a calculated orientation). This all works nice, except when I tried to make a loop (and I think I would get the same if i were to make the track go upside-down). At two points in the loop the track swings around 180 degrees very quickly and that isnt what I want, really. Does anyone know how to solve this? I suspect I need to change [0 0 1] to [0 0 -1] when the track goes upside down, but how do I determine when it does? Lantz [edited by - Lantz on May 5, 2003 12:28:54 PM]

One way is to have a second spline specifying your up direction at all times. This also has the advantage of easily being able to create banked tracks.

Hmm yea I guess that could be pretty smart. Although it may not be as simple to make the tracks with that as I probably will do them manually in some text-file or something. Right now I have a set of points where each point have an associated angle and that''s pretty easy to use when designing the tracks.

Does anyone else have any suggestion?