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vicky

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A student form Mumbai University, India


 

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09 Feb 2011 Inhull Efficient test for points inside a convex hull in n dimensions Author: John D'Errico

Thank you John for you valuable suggestions

08 Feb 2011 Inhull Efficient test for points inside a convex hull in n dimensions Author: John D'Errico

Hello John D'Errico,
I read your Inhull matlab file on File Exchange of MathWorks.com. I need a small help from you.

K = convhulln( X , { 'Qt' } );

each row of K contains the indices to the points defined in X, that makeup the triangular facet of the convex hull.
I want to find the outward normals to each of triangular facets in a direction pointing outwards from the convex hull. But I am stuck on how to determine the direction of the normal, whether it is outward or inward.

I think the indices in K (to the points of X) are stored in some meaningful manner(probably in counter clockwise). Here this is how am evaluating the outward normals for each triangular facets(not sure if this is correct way).

%outward normal to facet 1:
temp1 = X( K(1, 2) , : ) - X( K(1, 1) , : );
temp2 = X( K(1, 3) , : ) - X( K(1, 1) , : );
normal = cross( temp1, temp2 );

I need your valuable suggestions for this. I felt in your work, you have encountered this situation. Please guide me. I will be very thankfull for your help.

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