function tri = surftri ( p, t ) %*****************************************************************************80 % %% SURFTRI finds the surface triangles in a tetrahedral mesh. % % Discussion: % % The 2D version of this code is called BOUNDEDGES. % % Licensing: % % (C) 2004 Per-Olof Persson. % See COPYRIGHT.TXT for details. % % Reference: % % Per-Olof Persson and Gilbert Strang, % A Simple Mesh Generator in MATLAB, % SIAM Review, % Volume 46, Number 2, June 2004, pages 329-345. % % Parameters: % % Input, real P(NP,3), the coordinates of a set of nodes. % % Input, integer T(NT,1:4), a list of the nodes which make up each % tetrahedron in the mesh. % % % Form all faces, non-duplicates are surface triangles % faces = [t(:,[1,2,3]); t(:,[1,2,4]); t(:,[1,3,4]); t(:,[2,3,4])]; node4 = [t(:,4);t(:,3);t(:,2);t(:,1)]; faces = sort(faces,2); [foo,ix,jx] = unique(faces,'rows'); vec = histc(jx,1:max(jx)); qx = find(vec==1); tri = faces(ix(qx),:); node4 = node4(ix(qx)); % % Orientation % v1 = p(tri(:,2),:)-p(tri(:,1),:); v2 = p(tri(:,3),:)-p(tri(:,1),:); v3 = p(node4,:)-p(tri(:,1),:); ix = find(dot(cross(v1,v2,2),v3,2)>0); tri(ix,[2,3]) = tri(ix,[3,2]); return end