Continuous collision detection

Hi @hugo,

Sorry for the late reply. It looks like I don’t receive emails anymore when my messages are answered.

I made some progress in the last few weeks. I understood some things about how the freeAnimationLoop and the free positions work. I’m using the freeAnimationLoop with the LCPConstraintSolver. However, I don’t fully understand the math behind the constraint correction and how Delta v^cor is calculated. I’m also not sure what exactly the contacts’ values sent to the contact manager need to be and what the contactDistance does with collision responses using constraints.

My continuous detection almost works, but the times of intersection I calculate seems a little off. Sometimes the intersection falls just before or after the step, letting the objects penetrate even though the point and triangle visibly pass through each other. I wonder if it’s the numerical errors that propagate in the calculations, making the time of intersection a little off. In other cases, I detect an intersection and create a contact, but the constraint correction let the point and triangle penetrate anyway.

I would love to see this continuous collision plugin. Maybe it could help me figure out what I’m doing wrong. I’m available to Skype anytime.

Thank you,

François

Hi @hugo,

I saw that that the documentation improved a lot over the last few months. Thanks for all the work on this!

So far I made a discrete collision detection algorithm based on spatial subdivision that works well with the correct numerical settings (time step, alarm and contact distance). Now, I’m trying to adapt it to handle continuous collision detection. The idea is to compute the exact time of collision during the step (using linear interpolation of the vertices positions) and then to correct the positions so that the objects don’t go through one another. I’m using the free positions as the end-of-step positions for the linear interpolation. For the collision response, I’m trying to use constraints to correct the positions. It’s mostly this last part that is not clear to me.

Best,

François

Hi @hugo,

Sorry for the late reply. I didn’t work on this since July. I had not made progress in preventing objects to penetrate each others using constraints for collision response.

I’ll try to dive more into the theory and math of the solvers, Lagrange multipliers and constraints. I think I need this to understand the code. However, I’m running out of time since I’m supposed to graduate soon.

Do you know who’s familiar with this part of SOFA, and if it’s possible to discuss with them?

Thanks,

François

Hi @wzdy4444

I’ve been working on a collision algorithm for a simulation developed at my university. I’m not certain if Sofa has an implementation of continuous collision detection, but there is ways to integrate one with the freeAnimationLoop and the free positions. The part I’ve been struggling with is the response, where I try to use the Lagrange multiplier constraints. I don’t know what you are working on and what you are trying to test. If you tell me about it I might be able to help. Let me know if you have questions.

Regards,
Francois