Thread: [Algorithms] GJK -> contact set
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From: <Pau...@sc...> - 2004-08-31 10:36:15
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Hi There, Is there a nice way to go from a simplex to the contact set without having to clip? I keep thinking there must be something about the MS which we could use - it defines the contact plane (at the closest point) after all, with the features already on it. Failing that, could anyone go into more detail about the clipping method? Do you just project some vertices onto the contact plane to form 2d polygons? Which vertices do you choose and how do you tell the winding order? Cheers, Paul. ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify pos...@sc... This footnote also confirms that this email message has been checked for all known viruses. ********************************************************************** SCEE 2004 |
From: Erin C. <eri...@sb...> - 2004-09-01 06:06:49
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I don't know the answer yet to the first question. For box-box clipping using SAT, you determine the reference face associated with the separating axis. Then you find the incident face by finding the most parallel face. Now you have two oriented rectangles. You can now do 2D or 3D clipping: 2D clipping: project the incident face onto the reference face and then clip. Then map the resulting points back into 3D and throw away the ones that don't penetrate. 3D clipping: use 3D Sutherland-Hodgeman clipping of the incident face against the reference face and the side planes. I think this algorithm could be extended to handle convex polyhedrons without much difficulty. Some approximations might be necessary to get decent performance. Erin -----Original Message----- From: gda...@li... [mailto:gda...@li...] On Behalf Of Pau...@sc... Sent: Tuesday, August 31, 2004 3:36 AM To: gda...@li... Subject: [Algorithms] GJK -> contact set Hi There, Is there a nice way to go from a simplex to the contact set without having to clip? I keep thinking there must be something about the MS which we could use - it defines the contact plane (at the closest point) after all, with the features already on it. Failing that, could anyone go into more detail about the clipping method? Do you just project some vertices onto the contact plane to form 2d polygons? Which vertices do you choose and how do you tell the winding order? Cheers, Paul. ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify pos...@sc... This footnote also confirms that this email message has been checked for all known viruses. ********************************************************************** SCEE 2004 ------------------------------------------------------- This SF.Net email is sponsored by BEA Weblogic Workshop FREE Java Enterprise J2EE developer tools! Get your free copy of BEA WebLogic Workshop 8.1 today. http://ads.osdn.com/?ad_id=5047&alloc_id=10808&op=click _______________________________________________ GDAlgorithms-list mailing list GDA...@li... https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list Archives: http://sourceforge.net/mailarchive/forum.php?forum_id=6188 |
From: Alen L. <ale...@cr...> - 2004-09-01 07:22:38
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We don't use GJK, but we do use clipping of closest features (determined by SA instead of GJK). Our experience shows that it is not good enough to project vertices to the plane. Instead, we determine primary and secondary feature (primary is the one that generated the collision axis), and then clip the secondary feature against the primary one. In that process, we treat secondary feature as a 3d polygon, and the primary one as a prism you get by extending its polygon along the collision axis. So you have to clip against the collision plane, and against all edge-planes. This gives you minimal penetration depth for each resulting contact point. Otherwise you'd have same penetration depths for all points, what may cause less appealing collision response result, depending on your collision response solver, as some points might get pushed out more than it is needed. This is relatively simple if the two closest features are polygons. If you are working with cylinders or capsules, you have to handle their curved surfaces a bit differently, but it is based on the same assumption that it has to be in 3d, and that you need correct (minimal) penetration depths for each point. HTH, Alen ----- Original Message ----- From: <Pau...@sc...> To: <gda...@li...> Sent: Tuesday, August 31, 2004 10:35 Subject: [Algorithms] GJK -> contact set > Hi There, > > Is there a nice way to go from a simplex to the contact set without having > to clip? I keep thinking there must be something about the MS which we > could use - it defines the contact plane (at the closest point) after all, > with the features already on it. > > Failing that, could anyone go into more detail about the clipping method? > Do you just project some vertices onto the contact plane to form 2d > polygons? Which vertices do you choose and how do you tell the winding > order? > > Cheers, Paul. > > > ********************************************************************** > This email and any files transmitted with it are confidential and > intended solely for the use of the individual or entity to whom they > are addressed. If you have received this email in error please notify > pos...@sc... > > This footnote also confirms that this email message has been checked > for all known viruses. > > ********************************************************************** > SCEE 2004 > > > > ------------------------------------------------------- > This SF.Net email is sponsored by BEA Weblogic Workshop > FREE Java Enterprise J2EE developer tools! > Get your free copy of BEA WebLogic Workshop 8.1 today. > http://ads.osdn.com/?ad_id=5047&alloc_id=10808&op=click > _______________________________________________ > GDAlgorithms-list mailing list > GDA...@li... > https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list > Archives: > http://sourceforge.net/mailarchive/forum.php?forum_id=6188 > |