[ODE] Particle/cloth/skeleton (was: Re: Choleski factorization)

[Antonio_Martini@scee.net]

---------------------- Forwarded by Antonio Martini/CAMD/UK/SCEE on
24/03/2003 00:47 ---------------------------


Antonio Martini
24/03/2003 00:47

To:    "Martin C. Martin" <martin@metahuman.org>
cc:

Subject:    Re: [ODE] Particle/cloth/skeleton (was: Re: Choleski
       factorization)  (Document link: Antonio Martini)

>In practice, a
>dozen iterations seems to be more than enough, at least for simple
>systems.
the skeleton used in hitman was very simple(no neck, waist joints etc, no
twisting etc...)
and it required about 10 iterations if im not wrong. Further the
interactions i have seen in
the game were at very low speed(just moving dead bodies around at low
speed), which makes me
thinking that for high speed interactions many more iterations are
needed.Probably
the best way of evaluating such system is to implement it. Currently im
using an direct LCP solver +
iterative LCP solution + featherstone. months ago i implemented also a
cloth simulator that among many things
also enforces the length constraints the way you just said. From the
performances indications i have the particle method does not seem to be a
good substitute for more "classical" methods.
But it could be just my implementation.

further im not quite sure at how friction would work on a rigid bodies
modelled as pseudorandomnly
distribuited particles. We are talking about generic systems not only
simplified skeletons colliding against a static environment.
we may want skeletons to collide against each other or against other
objects, etc..After a collision as been detected the collision force can
only be applied at the available particles. not quite sure about
the all thing and clearly this part is missing in the Jakobseen paper.
Hitman doesnt' have generic
rigid body simulation if im not wrong.

however more detailed informations on the particles based approach can be
found on the Jeroen M. Wagenaar Phd(he worked on Hitman 1 and 2 if im not
wrong).






"Martin C. Martin" <martin@metahuman.org>@q12.org on 23/03/2003 22:47:36

Sent by:    ode-admin@q12.org


To:    Antonio_Martini@scee.net
cc:    ode@q12.org
Subject:    Re: [ODE] Particle/cloth/skeleton (was: Re: Choleski
       factorization)




Antonio_Martini@scee.net wrote:
>
> modeling rigid bodies as particles is rather unconvenient as they
generate
> really many constraints which in turn means that really many iterations
are
> needed
> in order to achieve an acceptable error(objects changing volume with
> highspeed impacts, etc..)
>
> Not to mention problems in the collision response. Talking about rigid
> bodies i would steer
> well away from that method.

Except that each constraint needs only 4 floating point multiplies and 1
division to enforce.  Which means you can simulate many, many iterations
quickly.  Also, ball-and-socket joints as well as hinge joints actually
reduce the number of particles with either reducing (hinge) or not
changing (ball-and-socket) the number of constraints.  In practice, a
dozen iterations seems to be more than enough, at least for simple
systems.  It can also be made adaptive, iterating until the error drops
below some specified value.

- Martin
_______________________________________________
ODE mailing list
ODE@q12.org
http://q12.org/mailman/listinfo/ode














Antonio Martini
Sony Computer Entertainment Europe
http://www.scee.com




**********************************************************************
This email and any files transmitted with it are confidential and
intended solely for the use of the individual or entity to whom they
are addressed. If you have received this email in error please notify
postmaster@scee.net

This footnote also confirms that this email message has been checked
for all known viruses.

**********************************************************************
 SCEE 2002