<div>ODE Documentation and examples :)</div>
<div> </div>
<div>Regards</div>
<div><br>Dan<br><br></div>
<div class="gmail_quote">On Wed, Jan 4, 2012 at 2:46 PM, Justin Clark-Casey <span dir="ltr"><<a href="mailto:jjustincc@googlemail.com">jjustincc@googlemail.com</a>></span> wrote:<br>
<blockquote style="BORDER-LEFT:#ccc 1px solid;MARGIN:0px 0px 0px 0.8ex;PADDING-LEFT:1ex" class="gmail_quote">Hi Teravus, nice to hear from you again!<br><br>Yes, more testing is needed, hopefully on OSGrid. But it seems there may be a tradeoff between having super smooth physics objects and being able to get more avatars in a scene without encountering cpu limits. My perception is having more avatars is a more common use case then lots of physics objects, particularly as OpenSim's current ODE use does not seem to provide a good physics simulation). Anybody who does want to try for better physics could always turn the collision number back up.<br>
<br>In any case, what was the rationale for choosing 80 as the default?
<div class="im"><br><br>On 03/01/12 22:30, Teravus Ovares wrote:<br></div>
<blockquote style="BORDER-LEFT:#ccc 1px solid;MARGIN:0px 0px 0px 0.8ex;PADDING-LEFT:1ex" class="gmail_quote">
<div class="im">With ODE, it depends on the physics situation.<br>With Tri-Mesh and the heightfield collider specifically, ODE generates lots of small effect contacts and then the<br>stepper integrates them all into a contact resolution force. With tri-mesh and the heightfield, depending on how an<br>
object collides with another, there could be 20 or 30 contacts that all factor into getting the object to react<br>normally. So, to test, you're going to want to use a stack of 'active'(physical in the client) tri-mesh objects. You<br>
may also want two or more trimesh LINKSETS to see how they react.<br>My guess, is the first thing that you're going to notice is that a tri-mesh object sitting on another object will become<br>more unstable (vibrate more). Each mini-contact represents a part of the force to keep the object from rotating from<br>
the other parts of the contact resolution force. As the effect gets worse, you're going to notice 'rotation anomolies'<br>that occur when objects collide.<br>Think of it like... you have a cube shaped trimesh... and the cube's corners are touching a flat ground. In<br>
theory, that would generate 4 contact points for each of the vertices touching the flat ground. If you cut one off,<br>then only three of the corners are being held above ground. On a larger scale, If you do that enough, then the<br>
object will partially fall through the ground and then bounce back up from an excessive contact resolution force<br>creating instability and vibrating.<br>Those are the indicators that I would use to determine if it's OK to make that change. Are 8 contacts enough for ODE<br>
to react properly in our usage? That remains to be seen :).<br>Regards<br>Teravus<br><br></div>
<div class="im">On Tue, Jan 3, 2012 at 4:58 PM, Adams, Robert <<a href="mailto:robert.adams@intel.com" target="_blank">robert.adams@intel.com</a> <mailto:<a href="mailto:robert.adams@intel.com" target="_blank">robert.adams@intel.com</a><u></u>>> wrote:<br>
<br> > ...<br> > According to [2], the maximum reported scripting collision contacts is 8.<br> ><br> > Testing with 8 on Wright Plaza today in the Tuesday meeting seemed to greatly reduce physics scene time compared to<br>
> previously without any apparent loss of required fidelity (50ms with 18 avatars, albeit mostly sitting down -<br> > unfortunately I didn't record previous week's numbers but they were higher. Nebadon tested one of his vehicles).<br>
<br> Looking at the code, contacts_per_collision is the number of collision points reported by ODE for each collision --<br> like a prim sitting on rough terrain and touching multiple places on the ground. Reducing the count to 8 means that<br>
no more than 8 contact points will be reported by ODE and, if there are more, you can't be sure you get the 'best' ones.<br><br> I suspect that most of the time there are only a few contact points so it doesn't make sense that reducing the<br>
number from 80 to 8 would significantly reduce the compute time. If it is the number of contact points causing the<br> computation overhead then ODE must be normally returning more than 8 contact points. Is this really the case? Or is<br>
something else going on?<br><br> -- ra<br> ______________________________<u></u>_________________<br> Opensim-dev mailing list<br></div> <a href="mailto:Opensim-dev@lists.berlios.de" target="_blank">Opensim-dev@lists.berlios.de</a> <mailto:<a href="mailto:Opensim-dev@lists.berlios.de" target="_blank">Opensim-dev@lists.<u></u>berlios.de</a>><br>
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<div class="im"><br>-- <br>Justin Clark-Casey (justincc)<br><a href="http://justincc.org/blog" target="_blank">http://justincc.org/blog</a><br><a href="http://twitter.com/justincc" target="_blank">http://twitter.com/justincc</a><br>
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