[SciPy-User] 3d convex hull

Ning Guo hhh.guo@gmail....
Mon Aug 29 02:36:21 CDT 2011

On Sunday, August 28, 2011 06:08 AM, Pauli Virtanen wrote:

It seems qhull does not output the vertices in a consistent order. I 
have to use the inner product of the normal with a side edge to 
determine the sign :-(

> Sat, 27 Aug 2011 23:12:24 +0800, Ning Guo wrote:
>> On Saturday, August 27, 2011 03:53 PM, Pauli Virtanen wrote:
> [clip]
>> Also, the formula to calculate normal may be like this:
>> face_normals[:,0] =
>> np.cross(tetra_points[:,0]-tetra_points[:,2],tetra_points[:,1]-tetra_points[:,2])
> [clip]
> Ah yes, exactly like that, my brain apparently wasn't working properly.
>> Regarding to the order of the vertices, I'm also not sure about their
>> convention. I'm trying to figure it out.
> If you find it out, please let us know, as this would be an useful thing
> to mention in the documentation. However, I'm not sure at the moment
> whether Qhull provides such ordering guarantees.

Geotechnical Group
Department of Civil and Environmental Engineering
Hong Kong University of Science and Technology
Clear Water Bay, Kowloon, Hong Kong

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