tively, the X, Y, and Z components of
               the ith vertex, where `i' ranges from 1 to nv.

               This routine doesn't associate units with the
               vertices.

      plates   is an array containing 3-tuples of integers
               representing the model's plates. The elements of
               `plates' are vertex indices. The vertex indices are
               1-based: vertices have indices ranging from 1 to
               nv.

               [3,np] = size(plates); int32 = clas