Something about Collidesurf

Hi All

I'm using kangaroo for some weaving things and i just find that it's really hard to make a rigid body in kangaroo. You should add some springs or Plaw.

When I find "Collidesurf", I just know that it will be a very useful tool!

But........................................the "Brep" that it support in Solid is really quite limited the pipe will cause a strange Bug that all points going to one position. Box is ok and I really want to know how about yours. All Brep is useful ?

Replies to This Discussion

Permalink Reply by Daniel Piker on July 7, 2011 at 8:01am

Hi Wuyi,

I can't replicate this bug - can you post the file ?

Collidesurf should work with any Brep, so long as it is closed (it needs to be able to check whether points are inside or outside)

Permalink Reply by Xiaoyi Wu on July 7, 2011 at 11:54pm

I just tried more times and there is a extremum existing.(Or just one value)

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Permalink Reply by Daniel Piker on July 9, 2011 at 6:07am

Ah, okay, I think I see part of the problem now.

CollideSurf is capable of either keeping points inside a volume (eg for packing problems), or outside (for solid collision like you have here).

The way it currently decides which one to use is based on where the particles start out at the beginning - if they are inside to begin with it keeps them inside, and if outside it keeps them outside.

When the radius of your pipes is going over a certain limit it is putting the points of that line inside them.

Would an option letting the user decide between containment or collision be helpful ?

So you could choose to make even points which start out inside stay on the outside (they would just immediately get forced to the outside)

Something else that might help will be putting in the option for force based collision. At the moment points get their position projected back onto the surface when they penetrate (and their velocity component normal to the surface reversed).

Force based would mean they just get pushed back towards the outside of the surface. This is slightly 'softer', and might help avoid the stability issues that seem to occur when changing Breps during simulation.

Permalink Reply by Xiaoyi Wu on July 9, 2011 at 7:38am

Thanks for Testing

I know the inside and outside thing, but did you try to change the radius to 60(not changing during simulation, before that). All the points should be outside the Brep but they don't. So I'm not sure about the problem is from my computer or files. It just goes wrong when radius is 60(just 60!), whether above or below is OK and everything goes well.

I think an option is good, but we should keep that easy and don't affect the whole system. Because these tiny option may cause some paradox.

Permalink Reply by Daniel Piker on July 9, 2011 at 7:52am

Hmm, very odd.

I don't think this issue is restricted to Kangaroo though - testing those points against those pipes for Brep inclusion gives false positives using the standard Grasshopper 'inside' component.

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