On Wed, 6 Feb 2002 07:31:52 +0100, "Apache"
<apa### [at] yahoocom> wrote:

> - yellow: collissions --> add springs to push atoms apart.

This approach gives rise to some problems:

1. It is a feedback approach, i.e. it corrects the error after it has
occurred. In this case, self-intersection may need several integration
cycles to be corrected, depending on inertia. Using a feed-forward
approach to predict self-collision early is definitely better, and
harder by a factor of [choose a random large number :)]

2. You need very stiff springs to improve the reaction time of the
collision avoidance algorithm, and this gives rise to very stiff
differential equations which need either a very small step to be
solved explicitly or an implicit integration routine of higher
complexity.

3. You do not account for friction between different parts of the
cloth, even if you do for the cloth-environment interface. I would
suggest using a feed-forward approach (collision prediction) to
identify imminent collisions. Then you'll have to decompose each
atom's velocity into normal and tangent to the plane tangent to the
cloth in the intersection point (this might prove difficult). Then
friction should be rather easy to apply, and as for self collision,
you'll probably want to apply penalties directly to the offending
atoms' velocities (i.e. cancel their normal component) rather then
introducing new springs into the problem.

Hope this helps. If you keep going at the pace you're currently doing,
you might as well get David Baraff's job at Pixar before the year is
over :) Good luck!


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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