[Opensim-dev] Update libode, or work towards better physics handling in this libode revision?

[Teravus Ovares]

No worries on the burden

To answer the question on tests/calibration..   I guess the purpose is
to set the variety of settings (and there are a plurality of them) to
produce reasonable physics results while using the least resources
possible in doing so.    It might be easy to configure in double
floating point mode, but we'd use twice to three times the CPU to
accomplish that.  Usually what I do is get it in a usable state with
high resource usage and scale the resource usage back until a balance
is acchieved.   This usually requires a lot of trial and error,
additionally, in the past, it has required the same process for each
platform (win/*nix/mac).

The first thing that I do is get collisions stable.   Avatar shouldn't
fall through the ground or shoot millions of meters into the air when
they log-in.

Next, I tune the avatar PID controller so it moves the avatar's
physics proxy effectively.  (un-tuned, you might see a result where
pressing a button causes you to go in the direction you want but with
a slow, curving direction change from from what seems like some random
direction)

After that, I find the best balance of frame frequency, collision
testing, contacts and contact friction..    and CPU usage while
testing against a very thin object in multiple directions. (tests to
ensure that I don't pass through a thin object at reasonable
velocities).

After that, I usually patch the libode library with some fixes that
apply to our use case.  In the past, superfluous asserts in the
library have caused random crashes. (Yes, I've tried to beat it over
the head of the ode developers and they insist on having them).  Also,
in the past, the heightfield collider needed a few patches to work
properly.  Without the patches, the ode library is very unstable.

After that, I usually work on more fine grained details, like llMove2Target.

This process needs to be done for windows platforms and usually also
has to be done for *nix platforms.   Furthermore, Mac platforms often
need a few small tweaks after that, but most of the *nix platform
settings apply.

This is a relatively long process of starting the simulator, fixing
something, stopping it..    starting it over again..  tweaking
something, stopping it..   over and over until it's right.   There's
some math involved in finding what fps/collision detection settings
/could possibly/ be good, but a lot of it is just, trial and error.

Best Regards

Teravus


On 10/7/08, Dr Scofield <DrScofield at xyzzyxyzzy.net> wrote:
> Teravus Ovares wrote:
> > ok, so far, 2 for update, 0 for current lib.
>
> +1 for update --- but i'm kind of feeling bad saying that because that places a
> tremendous burden on you...
>
> --
> dr dirk husemann ---- virtual worlds research ---- ibm zurich research lab
> SL: dr scofield ---- drscofield at xyzzyxyzzy.net ---- http://xyzzyxyzzy.net/
> RL: hud at zurich.ibm.com - +41 44 724 8573 - http://www.zurich.ibm.com/~hud/
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