VERTEXNORMAL Compute normals to a mesh vertices.

   N = vertexNormal(V, F)
   Computes vertex normals of the mesh given by vertices V and F. 
   V is a vertex array with 3 columns, F is either a NF-by-3 or NF-by-4
   index array, or a cell array with NF elements.

   Example
     % Draw the vertex normals of a sphere
     s = [10 20 30 40];
     [v f] = sphereMesh(s);
     drawMesh(v, f);
     view(3);axis equal; light; lighting gouraud;
     normals = vertexNormal(v, f);
     drawVector3d(v, normals);

   See also
     meshes3d, meshFaceNormals, triangulateFaces

 ------
 Author: David Legland
 e-mail: david.legland@grignon.inra.fr
 Created: 2011-12-19,    using Matlab 7.9.0.529 (R2009b)
 Copyright 2011 INRA - Cepia Software Platform.

Package: matgeom