## Search found 23 matches

- Wed May 10, 2017 8:23 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Johnson's distance algorithm: can't find smallest simplex
- Replies:
**4** - Views:
**2070**

### Re: Johnson's distance algorithm: can't find smallest simple

Hi Gino, At this point I'm thinking of doing as suggested by Christer in his book, checking the origin against the Voronoi regions of the simplex and choosing the closest feature that way. While mathematically equivalent to Johnson's algorithm, a number of people have said it can help alleviate num...

- Sun May 07, 2017 7:56 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Johnson's distance algorithm: can't find smallest simplex
- Replies:
**4** - Views:
**2070**

### Re: Johnson's distance algorithm: can't find smallest simple

Hi Adrian, I haven't checked your code so I cannot tell whether there is a bug in there. I do know that due to rounding issues it can happen that no proper simplex is found. In fact, the original paper by Gilbert Johnson and Keerthi already mentions the issue and offers a solution in form of backup ...

- Sun Dec 07, 2014 11:02 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Continuous GJK for spherically extended objects
- Replies:
**1** - Views:
**2435**

### Re: Continuous GJK for spherically extended objects

Is there a way to perform a ray cast as described in Gino Van Den Bergen's Ray Casting against General Convex Objects , against spherically extended objects without having to calculate support points for the enlarged objects? With GJK you can adjust the termination condition to account for the slig...

- Tue Jun 23, 2009 2:01 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Bullet's Voronoi Simplex Solver
- Replies:
**46** - Views:
**28704**

### Re: Bullet's Voronoi Simplex Solver

What you are suggesting is when only polytopes are used, you can do without the closest point computation, or at least you can skip all intermediate closest point computations and keep only the final one. Termination can be governed by detection of a repeated support point (vertex of the CSO, not ve...

- Thu Mar 12, 2009 10:43 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Expanding Polytope Algorithm
- Replies:
**2** - Views:
**2365**

### Re: Expanding Polytope Algorithm

In principle, your approach could work for a pair of convex polytopes. However, since the boundary of the configuration space obstacle (Minkowski difference) of the polytopes may contain quadrilaterals it could very well happen that EPA cycles between two (or more) faces. Progressive growth of the e...

- Tue Jun 12, 2007 1:00 pm
- Forum: Links, Papers, Libraries, Demos, Movies, Comparisons
- Topic: Rotational penetration depth
- Replies:
**5** - Views:
**4389**

### Re: EPA and PD^g

We claimed that the EPA is not exact in the following sense (neither do ours, DEEP): 1) It is not an analytical solution so that it cannot provide all PD solutions; e.g. imagine a sphere overlapped with itself; it has an infinite # of solutions to report, which the EPA cannot. 2) The result of EPA ...

- Tue Apr 11, 2006 9:02 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Contact Manifold Generation: A question about GJK
- Replies:
**16** - Views:
**31031**

Taking the closest features of the last-found simplices (sets of support points) for the two objects tested using GJK gives you a rough approximation of the contact manifold but you can do better, since (a) this simplex is usually not the complete manifold and (b) it is not necessarily a face of the...

- Sat Mar 25, 2006 3:27 am
- Forum: Non-technical forum and license/patent discussion
- Topic: Zlib/MIT/LGPL/GPL Collision Detection Library License
- Replies:
**8** - Views:
**16734**

### Re: Computing distance

SOLID 3.5 computes both the distance and the penetration depth for any combination of convex shape types. SOLID 3.5 can be downloaded from http://www.dtecta.com. Cheers, Gino but it is not free,right?I think FreeSolid is better . This depends on your definition of freedom. GPL is a little more rest...

- Sun Mar 19, 2006 6:19 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Computing distance
- Replies:
**6** - Views:
**4909**

### Re: Computing distance

Hi! Anyone know of algorithm that compute the distances between two bodies as well as the penetration depth? Could I modify Bullet to get the distances? I need that distance because some time steppers use "prevent penetration" not "penetration correction" approach, so the distances are needed. I'd ...

- Mon Feb 06, 2006 12:24 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Gino's Book - Robustness section
- Replies:
**4** - Views:
**4009**

Using exact arithmetic sub would be 4e-8 but with floating-point arithmetic it is quite far from it ( see above ). So, I guess that this turned out to be a catastrophic cancellation situation because both results ( from floating-point and exact arithmetic ) don't have any digits in common, therefor...

- Fri Feb 03, 2006 4:20 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Gino's Book - Robustness section
- Replies:
**4** - Views:
**4009**

### Re: Gino's Book - Robustness section

So, from page 59 I'm not understanding what Gino is trying to explain in the phrase that starts with "Assume". Hope that helps to clarify what's meant. Well put. Thanks Christer. The only thing I'd like to add is that computations would still classify as 'fairly accurate' if |ei| <= C * u for C gre...

- Wed Nov 23, 2005 8:18 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Kinetic Sweep and Prune
- Replies:
**8** - Views:
**15011**

The kinetic sweep and prune method, however, seems to maintain a consistent motion description, whereas in the 4D broad phase from my presentation the new target positions are set for each moving object in each time step. That's interesting... we don't need/use time steps, though we permit them if ...

- Tue Nov 22, 2005 3:05 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Kinetic Sweep and Prune
- Replies:
**8** - Views:
**15011**

For multi-body continuous motion Gino presented the 4D SAP Broadphase, please read page 47 and onwards in this presentation: https://www.cmpevents.com/Sessions/GD/ContinuousCollisionDetection1.ppt - How does the Kinetic Sweep and Prune compare to this 4D SAP Broadphase? At first glance they seem si...

- Tue Oct 11, 2005 9:17 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Barycentric coordiantes and voronoi solver
- Replies:
**8** - Views:
**8225**

### Re: Barycentric coordiantes and voronoi solver

Which GJK implementation requires more information from the simplex solver, and how does it use this exactly, JMC ? Erwin The whole reason I brought this up was because SOLID uses the values even in the case that the simplex is full. Look at SOLIDs common_point and closest_points in DT_Convex.cpp. ...

- Tue Oct 04, 2005 3:44 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Questions for Gino about your book
- Replies:
**3** - Views:
**4618**

4) Could you describe the is_affinely_dependant test, and why you added that to your code. It isn't mentioned in the book at all. Thanks This test checks whether the current simplex W cup { w } has a zero "volume". Here "volume" means length (line segment), area (triangle) or volume (tetrahedron). ...