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Create an oriented bounding box from vertices

Posted on 2009-05-04
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Last Modified: 2013-12-17
Hi there,

I'm doing this in XNA but it shouldn't be too different in DirectX
I'm getting the vertices of a box mesh from the vertexbuffer, now from those vertices I'd need to recreate that box as an oriented bounding box.
This is my code, in transformedvertices my vertices are stored in world space, a total of 24, now I'd need to be able to turn that into an oriented bounding box.
Anyone have any ideas?

Thanks in advance.
ModelMeshPart part = modelmesh.MeshParts[j];
                n = part.NumVertices;
 
                VertexPosition[] vertices = new VertexPosition[part.NumVertices];
 
                modelmesh.VertexBuffer.GetData<VertexPosition>(part.BaseVertex * part.VertexStride, vertices, 0, part.NumVertices, part.VertexStride);
 
                int t = MySkinnedModel.SkeletonBones.Count;
                string[] names = new string [t];
 
                for (int p = 0; p < t; p++)
                { 
                    names[p] = MySkinnedModel.SkeletonBones[p].Name.ToString();
                }
 
                Vector3[] transformedvertices = new Vector3[(part.NumVertices)];
 
                Matrix transformmatrix = MyAnimationController.SkinnedBoneTransforms[0];
 
                for (int i = 0; i < part.NumVertices; i++)
                {
                    transformedvertices[i] = Vector3.Transform(vertices[i].Position, transformmatrix);
                }

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Question by:Snapples
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ikework earned 1500 total points
ID: 24302428
hi Snapples,

this might be interesting for you:

http://codesuppository.blogspot.com/2006/06/best-fit-oriented-bounding-box.html

another technique is to compute a covariance-matrix of the point-cloud to compute the bounding box.

ike
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by:Snapples
ID: 24325501
Thanks for the link, I hadn't seen that one yet. Unfortunately it's of no use to me, I should have mentioned this. The bounding box surrounds part of an animated mesh, so the box has to be updated every frame. The code in your link is too performance heavy to run every single frame.
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Expert Comment

by:ikework
ID: 24326621
ok i see .. did you try the covariance-matrix yet?
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by:Snapples
ID: 24347474
I found the solution I needed.

In my OBB class, I have a global Vector3[24] array, in the constructor I fill it with the VertexBuffer of my mesh. I also have an Edge and a Quad struct, which has 2 and 4 short values in which I store the IndexBuffer values of the edges and faces. So basically storing every vertex, edge, face and quad with a minimum of data. Every frame I just have to transform the Vector3 array with the transformation matrix of the bone.
Then to check for collision I check if any of the edges of box1 collide with any faces of box2.

But thank you ike, I did get a lot of help from that first link you posted.
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by:ikework
ID: 24348308
great to hear that .. good luck .. :)
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