For a physics object, what exactly determines the bounding volume?

How does SL calculate the bounding volume for a physical object. (I should really say "Havoc" instead of SL...) I am curious, because I have a vehicle I have created which, uh, likes to bounce me back and forth between three or four sims when I use it.

In fact, when I rez the vehicle in the world, it sits and twitches slightly, as if it is constantly trigger collisions. It doesn't matter if I rez it on perfectly flat terrain or a large 10x10x10 box. It's almost as if the primset has a TON of pent up energy in it that get somehow released when I occasionally hit a wall or other sort of surface.

I've merely bumped a wall (and not even a sloped one) and have been sent on vast astral journies...

I am <i>guessing</i> that the way I have the prims linked is causing this. If I unlink all the prims and then just use a giant box instead with the script that I am using (it's a car, BTW) -- Everything works just fine. So I don't think it's the actual vehicle parameters causing the problem.

So, to summarize what I am asking is -- Interpenetration seems to be fine for linked objects in a physical set, so I am guessing that SL generates a single bounding volume for the primset. What determines how this bounding volume is created? Does the linking order matter? (ie: Does the root prim set the overall shape, and then each additional prim is added to the bounding volume?) Heck, can I turn on bounding volume view under the Debug menu?

My vehicle works fine, other than it never sits still (always twitches) and occasionally bounces me into the middle of walls, where I can only teleport to escape... ^_^

Info regarding Havok 1 physics precision.

http://secondlife.com/badgeo/wakka.php?wakka=precision

Some info regarding the 'bounding box'. There is actually no such thing as a bounding box.

http://secondlife.com/badgeo/wakka.php?wakka=BoundingBox

Also, sometimes the havok engine isn't too happy calculating prims which are excessively twisted, misshapen or thin colliding with the ground or other prims. Another reason why you shouldn't drag women with prim hair from their legs? Just kidding.

Appearently, I have one (or more) of those "bad prims" in my vehicle. I've stripped everything out of the vehicle and just turned it into a large box -- attached the scripts, and viola, everything works just fine.

I have been adding in the vehicle prims one by one, in hope of finding what exactly is causing it to go all wonky, but this is slow going. At least I now sorta know why it's acting like it is.

Interesting that Havoc uses actual surface for collision detection. I'm sure it's probably internally turning those prims into convex hulls, which considering all the weird ways you can convolute prims is why it's kinda unpredictable. I'm just guessing, though.

What would be nice would be a llSetCollisionPrim(link_number), which let us select which prim to use for collision detection -- then it could ignore the rest of the prims in the linkset. Just dreaming though.

I think thats a great idea, being able to selectively choose which prims are used for collision calculations. I think it should be part of the build tools though. So that when you link a set of physics enabled prims, you can go 'edit linked parts' to change individual prims to 'calculate collision', thus allowing higher primmed vehicles instead of the dismal 31. This is similar to avatars, which are physics objects themselves but has attachments which do not get factored in collission calculations.

WOW!!! Those are really hairy legs!

hurtz too!

I haven't had problems with this yet, but can't you just set the parts you don't want to collide phantom?

LOL. Another reason why you shouldn't drag men in drag with prim hair from their legs? Sorry english isn't my first language.