void border_node(Halfedge_iterator eitr, Point& ept, Point& vpt) {
Point& ep1 = eitr->vertex()->point();
Point& ep2 = eitr->opposite()->vertex()->point();
ept = Point((ep1[0]+ep2[0])/2, (ep1[1]+ep2[1])/2, (ep1[2]+ep2[2])/2);
Halfedge_around_vertex_circulator vcir = eitr->vertex_begin();
Point& vp1 = vcir->opposite()->vertex()->point();
Point& vp0 = vcir->vertex()->point();
Point& vp_1 = (--vcir)->opposite()->vertex()->point();
vpt = Point((vp_1[0] + 6*vp0[0] + vp1[0])/8,
(vp_1[1] + 6*vp0[1] + vp1[1])/8,
(vp_1[2] + 6*vp0[2] + vp1[2])/8 );
}
