[Opensim-dev] density

[Dahlia Trimble]

I'm trying to imagine the consequences of having the wrong density for an
avatar. The most common physics application that I'm aware of for avatars
are flight assists, which may be less common in OpenSim as there is no
flight ceiling. Another application may be push type teleporting systems.
Applications which require accurate physics usually use the results of
llGetMass() as a term for any calculations which could lessen the need for
accurate default density.
It is a problem that many of the values for physics are empirically derived,
and that there are so many variations across implementations, such as the
differences between 32 and 64 bit systems and between different 64 bit
systems. This suggests that any deviation from the established values may
need to be a configuration option (if they aren't already), and that some
experiments may need to be designed and carried out to determine optimum
values. Perhaps, if all of the important values would be user-configurable,
a procedure could be developed for calibrating the physics engine for any
given installation?


On Sun, Mar 22, 2009 at 3:03 PM, Charles Krinke <cfk at pacbell.net> wrote:

> We have m_density defined in two different places with two different
> values.
>
> One is in: ...\OpenSim\Region\Physics\OdePlugin\ODECharacter.cs - (72, 22)
> :
>
> public float m_density = 60f;
>
> Another is in:
> ...\OpenSim\Region\Physics\OdePlugin\ODEPrim.cs(152):
>
>  private float m_density = 10.000006836f; // Aluminum g/cm3;
>
> And in looking at the usage to calculate mass, it looks like the math is
> right, but yet, the avatar seems to have a higher density then the prim.
>
> I know that these are empirically determined, but in trying to look forward
> to a world where we actually might use the density of metal, rubber, glass,
> rock, plywood to do some additional physics *stuff*, it seems that we might
> want to see if we can harmonize our notion of density a little bit.
>
> Perhaps I am just missing the boat here. But, I would like to understand
> how we might be able to move forward a little bit on density some time.
>
> Charles
>
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