I’ve been working on a book review in my spare time for the past week, so I’ll relieve the suspense and get the final post up next week sometime.

]]>I have run into a similar problem with our spline code. I wanted to take splines and drive a rigid body along it. Now there are two modes that I considered. The first is where a constraint is pushing the body along the spline according the original authored velocity.

The second, more interesting mode, is where the body can slide along the spline according to gravity, like a roller coaster. This works well until the spline has a point of zero velocity, because the constraint equations need a tangent vector. My solution? I decided to view this as a degeneracy and require that spline always have nonzero velocity. How nice!

Anyhow, I just found your blog and thought it was interesting that you ran into a similar problem.

]]>