Search found 38 matches
- Thu Apr 17, 2014 6:32 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: GJK/EPA and hollow shapes
- Replies: 2
- Views: 7818
Re: GJK/EPA and hollow shapes
It's perhaps similar, but I'd be very surprised if you couldn't get GJK/EPA to work with some modification. I don't think the Minkowski difference is usable, but some sort of erosion CSG type thing might work instead? It should still produce a convex region, which you should still be able to walk wi...
- Mon Apr 14, 2014 11:17 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: GJK/EPA and hollow shapes
- Replies: 2
- Views: 7818
GJK/EPA and hollow shapes
Is there a way to leverage GJK or EPA for hollow shapes? Imagine this case: triangleInsideSquare.png You want to keep the red triangle inside the black square. In the case in the picture you'd want there to be no collision. But vertex A is *almost* touching the edge, so the distance/separating vecto...
- Wed Feb 05, 2014 5:53 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Continuous distance function
- Replies: 2
- Views: 7397
Re: Continuous distance function
Yeah, that's actually the approach I'm exploring right now. I'm sort of off on my own in left field at the moment, though, so I'm looking for some perspective.
- Mon Feb 03, 2014 7:52 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Looking for research topics in areas of realtime physics
- Replies: 10
- Views: 19393
Re: Looking for research topics in areas of realtime physics
As a motivating example, imagine a mass of 1e5 kg resting on top of a mass of 1e-5 kg resting on top of the floor. What's the force that the smaller body has to deliver to the larger body to keep it from falling down? Basically gravity * 1e5. And then, by Newton's third law, what's the force that t...
- Sun Feb 02, 2014 1:42 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Help building Jacobian using partial derivative
- Replies: 3
- Views: 11753
Re: Help building Jacobian using partial derivative
Yes, I'm familiar with that approach. I was specifically interested in getting comfortable with the mathematics, though. I'm going to be exploring building the hessian matrices of a reduced coordinate system, which is a much harder problem! So I wanted to exercise my math chops and make sure I can d...
- Sat Feb 01, 2014 10:06 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Continuous distance function
- Replies: 2
- Views: 7397
Continuous distance function
I'm working on a collision detection algorithm, and I'm looking for alternatives to GJK for calculating the "distance" between two convex polyhedra. At this point performance isn't a concern, as it's very speculative research. Instead, I want these basic properties: 1. The distance functio...
- Sat Feb 01, 2014 9:38 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Help building Jacobian using partial derivative
- Replies: 3
- Views: 11753
Re: Help building Jacobian using partial derivative
Ah, hmm, I think I figured it out. d cos θ(t) -sin θ(t) * dθ(t) ---------- = ------------------- = -sin θ(t) dθ(t) dθ(t) That is, I'm not finding the derivative with respect to time, but with respect to θ(t). So the derivatives on the top and bottom cancel, and w drops out of my Jacobian.
- Fri Jan 31, 2014 5:40 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Looking for research topics in areas of realtime physics
- Replies: 10
- Views: 19393
Re: Looking for research topics in areas of realtime physics
That wouldn't help actually. The core of the problem is that the mass matrix's condition number (basically your largest mass divided by your smallest mass) gets propagated to the larger equation. You need to find the inverse of that matrix, and inverting a matrix with a large condition number is ill...
- Fri Jan 31, 2014 1:08 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Looking for research topics in areas of realtime physics
- Replies: 10
- Views: 19393
Re: Looking for research topics in areas of realtime physics
A good way of handling collision response between bodies with vastly different mass ratios would be a reasonable project. It's not that it's an open problem so much as it's an unexplored problem. The onus is usually on the users to make the system less extreme by tweaking the masses. See, eg, this p...
- Thu Jan 30, 2014 9:03 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Help building Jacobian using partial derivative
- Replies: 3
- Views: 11753
Help building Jacobian using partial derivative
I'm trying to get my mathematical ducks in a row and finally tackle building Jacobians for a constraint using partial derivatives. In the past I've sort of messed around with what I want the constraint to do in velocity space and built up the Jacobian that way. But this time I'd like to tackle doing...
- Mon Jan 06, 2014 9:21 pm
- Forum: Links, Papers, Libraries, Demos, Movies, Comparisons
- Topic: Journals for continuous collision detection?
- Replies: 3
- Views: 51738
Re: Journals for continuous collision detection?
Hmm, would it be fair to say that research isn't disseminated via papers/articles then? Most of the new work I'm familiar actually does come from blogs and the like.
- Mon Jan 06, 2014 5:51 pm
- Forum: Links, Papers, Libraries, Demos, Movies, Comparisons
- Topic: Journals for continuous collision detection?
- Replies: 3
- Views: 51738
Journals for continuous collision detection?
I'm curious what journals articles on continuous collision detection have shown up in? As far as I know, there aren't any specifically for CCD, so they tend to get written up in ones for graphics, like SIGGRAPH papers and the like. The small library of articles I'm aware of tend to be 15+ years old,...
- Thu Feb 28, 2013 12:37 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Resting Contact: Relative Velocity < Impulse Threshold
- Replies: 4
- Views: 9689
Re: Resting Contact: Relative Velocity < Impulse Threshold
They're just tuning values. They don't necessarily correspond to any real values for things (the damping and spring constants for resting contacts have real world analogies, except that resting contacts aren't really springs, so again the values are just for tuning). Play with the values until you g...
- Mon Feb 25, 2013 9:55 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Physics Shader - Just a thought
- Replies: 6
- Views: 12898
Re: Physics Shader - Just a thought
The problem with that is that physics is a global phenomenon, so it doesn't lend itself well to massively parallel execution. By contrast, one triangle/pixel renders pretty much the same as another, regardless of what the other elements are doing. There are a few serial elements to rendering, though...
- Thu Feb 16, 2012 9:07 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Purpose of this sub forum
- Replies: 3
- Views: 5712
Re: Purpose of this sub forum
I like the red text I'm sure there'll still be some but hopefully this lowers the number at least. The rest should be manageable by moving the threads.