Simplify btConvexHullShape?

[SteveDeFacto]

I have a point cloud with too many vertices and it's convex hull is too elaborate. I would like to simplify the convex shape that is generated by the constructor for btConvexHullShape but I have no idea how to do this?

[Pyritie]

use a simpler model?

EDIT:
if you can't do that, maybe weld vertices that are close together within a certain threshold?

[eagletree]

I had this in my notes. I think it came from the Wiki. Haven't tried it yet but eventually I was going to need it. Maybe this is what you mean? I'm just parroting, interested to know if it works.

reduces the number of vertices to a minimum before using convexhullshape. Example is in bullet/demos/convexdecompositiondemo

Code: Select all

//	btConvexShape* originalConvexShape; is the original convexHullShape

	//create a hull approximation
	btShapeHull* hull = new btShapeHull(originalConvexShape);
	btScalar margin = originalConvexShape->getMargin();
	hull->buildHull(margin);
	btConvexHullShape* simplifiedConvexShape = new btConvexHullShape(hull->getVertexPointer(),hull->numVertices());

[dphil]

Yes the btShapeHull is one way to go. It simplifies a convex hull using a 42-point sphere, resulting in a convex hull of 42 points, or sometimes less (based on my own experimentation). I looked into this when checking out the new HACD decomposition library in Bullet, to simplify produced convex hulls. However, after experimenting, it seemed to me that the HACD library's own hull simplification tools did a better job of hull conservation vs num vertices trade-off. But in general, btShapeHull should be decent.

[SteveDeFacto]

I had this in my notes. I think it came from the Wiki. Haven't tried it yet but eventually I was going to need it. Maybe this is what you mean? I'm just parroting, interested to know if it works.

reduces the number of vertices to a minimum before using convexhullshape. Example is in bullet/demos/convexdecompositiondemo

Code: Select all

//	btConvexShape* originalConvexShape; is the original convexHullShape

	//create a hull approximation
	btShapeHull* hull = new btShapeHull(originalConvexShape);
	btScalar margin = originalConvexShape->getMargin();
	hull->buildHull(margin);
	btConvexHullShape* simplifiedConvexShape = new btConvexHullShape(hull->getVertexPointer(),hull->numVertices());

This idea does appear to have worked!

[Flix]

[btShapeHull] reduces the number of vertices to a minimum before using convexhullshape. Example is in bullet/demos/convexdecompositiondemo

Good to know. Now I understand what dphil meant in another post .
I've added this feature to my HACD demo here http://bulletphysics.org/Bullet/phpBB3/ ... =17&t=7159, although I agree that HACD itself does a better job in most cases in reducing the number of hull vertices.

[SteveDeFacto]

[btShapeHull] reduces the number of vertices to a minimum before using convexhullshape. Example is in bullet/demos/convexdecompositiondemo

Good to know. Now I understand what dphil meant in another post .
I've added this feature to my HACD demo here http://bulletphysics.org/Bullet/phpBB3/ ... =17&t=7159, although I agree that HACD itself does a better job in most cases in reducing the number of hull vertices.

Yeah, I ended up reverting back to my engine's reduction algorithm. It's just not quite good enough for my uses.