# [ODE] Combining contact surface parameters

Graham Fyffe gfyffe at gmail.com
Mon Feb 28 22:12:21 MST 2005

```Personally I go with a sqrt(a * b) approach.  That way 0.5 vs 0.5
gives you 0.5, and 0.0 vs 1.0 gives you 0.0.  All desirable.  It's
still a grossly simplistic hack, but it works well enough for me :)

- Graham

On Mon, 28 Feb 2005 18:16:48 -0800, Marco Grubert <mgrubert at conitec.net> wrote:
> Rubber (1.0) on ice (0.0) would still slide that's why I use the multiply
> approach..
>
> - Marco Grubert
>
> ----- Original Message -----
> From: "Alex Rubinsteyn" <rubnstyn at uiuc.edu>
> To: <ode at q12.org>
> Sent: Monday, February 28, 2005 17:59
> Subject: [ODE] Combining contact surface parameters
>
> >I know this has come up on this list before, but I couldn't find any sort
> >of
> >
> > When colliding two geoms with different contact surfaces parameters, what
> > is
> > the most realistic (in appearance) method of combining their surfaces?
> >
> > The suggestions I've seen were:
> >
> > 1) having a lookup table for all combinations of surfaces
> > 2) averaging values (1st mu = 0.1, 2nd mu = 0.9, collision mu = 0.5)
> > 3) multiplying values ( 1st mu = 0.1, 2nd mu = 0.9, collision mu = 0.09)
> >
> > The first is impossible for me, since I won't know what all the possible
> > surfaces
> > will be in advance.
> > So between averaging and multiplying, what gives better results?
> > Is there some other method? (taking the max/min for some parameters?)
> >
> > Thanks,
> > Alex
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```