particles in physics, was RE: [Algorithms] Computing the penetrat ion distance

[Mat N. <mat...@mi...>]

To be really robust for your penalty methods you should base them off of
penetration volume, not necessarily penetration depth.

As a quick aside, anyone done any work integrating particle systems w/ their
rigid body engines? I'm taking the partitioned dynamics approach, as it
seems to be the best overall design (decoupled simulations w/ a minor
accuracy hit). http://www.cs.cmu.edu/~baraff/papers/partition-tr.pdf

I'm a paper junkie, I admint it :)

MSN

P.S. BTW, everyone, it's Mat, not Matt.

-----Original Message-----
From: Pierre Terdiman [mailto:p.t...@wa...]
Sent: Thursday, October 12, 2000 12:26 PM
To: gda...@li...
Subject: Re: [Algorithms] Computing the penetration distance


Uh, and I missed it ? ....ahem. Thanks.

Else I think I can do something like that:
1) on collision, compute the closest points P and Q, and the separating
plane H from previous frame
2) compute two planes parallel to H, one of them contains P's new position,
the other contains Q's new position
3) reflect the two objects through the two planes
4) compute the closest points with GJK, for the two reflected objects. The
penetration distance is the distance between those two new closest points.

Now, the problem is to do 3) efficiently, discarding some useless vertices
on the fly so that 4) is fast as well.

Pierre

----- Original Message -----
From: Jamie Fowlston <j.f...@re...>
To: <gda...@li...>
Sent: Wednesday, October 11, 2000 9:48 PM
Subject: Re: [Algorithms] Computing the penetration distance


> There's a modified GJK which returns penetration under some circumstances;
bit
> rushed for time at the mo, but I think you can get it (or at least
something
> relatedly interesting :) from
>
> http://users.comlab.ox.ac.uk/stephen.cameron/distances.html
>
> 3rd reference.
>
> Jamie
>
>
> Pierre Terdiman wrote:
>
> > Ok,
> >
> > Before diving into the funny hell of LCP programs and all those painful
> > little things, I'd give penalty methods a chance - à la David Wu. So, I
need
> > to estimate (or better, compute accurately) the penetration distance
> > between, say two convex polytopes, even if it would be better if I were
able
> > to derive it for any pair of non-convex objects.
> >
> > GJK gives you the closest-points and the exact distance when no
collision
> > occurs. But all bets are off when the polytopes collide. I've looked
into my
> > archives, and I don't have the faintest, slightest, little reference
> > regarding that topic. Hence, before cooking up my own wacked solution, I
> > feel obliged to ask the list : would you have one or two links for
me...?
> >
> > Thanks, list.
> >
> > Pierre
> >
> > PS: don't bother telling me to forget penalty methods.
> >
> > _______________________________________________
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> > http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list
>
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