\( \newcommand{\E}{\mathrm{E}} \) \( \newcommand{\A}{\mathrm{A}} \) \( \newcommand{\R}{\mathrm{R}} \) \( \newcommand{\N}{\mathrm{N}} \) \( \newcommand{\Q}{\mathrm{Q}} \) \( \newcommand{\Z}{\mathrm{Z}} \) \( \def\ccSum #1#2#3{ \sum_{#1}^{#2}{#3} } \def\ccProd #1#2#3{ \sum_{#1}^{#2}{#3} }\)

CGAL 4.8 - CGAL and the Boost Graph Library

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BGL_polyhedron_3/normals.cpp
#include <fstream>
#include <boost/graph/graph_traits.hpp>
#include <CGAL/property_map.h>
#include <CGAL/basic.h>
#include <CGAL/Kernel/global_functions.h>
// Polyhedron
#include <CGAL/Cartesian.h>
#include <CGAL/Polyhedron_3.h>
#include <CGAL/IO/Polyhedron_iostream.h>
#include <CGAL/Polyhedron_items_with_id_3.h>
// Graph traits adaptors
#include <CGAL/boost/graph/graph_traits_Polyhedron_3.h>
typedef CGAL::Cartesian<double> Kernel;
typedef Kernel::Point_3 Point;
typedef Kernel::Vector_3 Vector;
typedef CGAL::Polyhedron_3<Kernel, CGAL::Polyhedron_items_with_id_3> Polyhedron;
template<typename HalfedgeGraph,
typename PointMap,
typename NormalMap>
void calculate_face_normals(const HalfedgeGraph& g,
PointMap pm,
NormalMap nm)
{
typedef boost::graph_traits<HalfedgeGraph> GraphTraits;
typedef typename GraphTraits::face_iterator face_iterator;
typedef typename GraphTraits::halfedge_descriptor halfedge_descriptor;
typedef typename boost::property_traits<PointMap>::value_type point;
typedef typename boost::property_traits<NormalMap>::value_type normal;
face_iterator fb, fe;
for(boost::tie(fb, fe) = faces(g); fb != fe; ++fb)
{
halfedge_descriptor edg = halfedge(*fb, g);
halfedge_descriptor edgb = edg;
point p0 = pm[target(edg, g)];
edg = next(edg, g);
point p1 = pm[target(edg, g)];
edg = next(edg, g);
point p2 = pm[target(edg, g)];
edg = next(edg, g);
if(edg == edgb) {
// triangle
nm[*fb] = CGAL::unit_normal(p1, p2, p0);
} else {
// not a triangle
normal n(CGAL::NULL_VECTOR);
do {
n = n + CGAL::normal(p1, p2, p0);
p0 = p1;
p1 = p2;
edg = next(edg, g);
p2 = pm[target(edg, g)];
} while(edg != edgb);
nm[*fb] = n / CGAL::sqrt(n.squared_length());
}
}
}
int main(int, char** argv)
{
typedef boost::property_map<
Polyhedron,
CGAL::face_index_t
>::const_type Face_index_map;
std::ifstream in(argv[1]);
Polyhedron P;
in >> P ;
// initialize facet indices
std::size_t i = 0;
for(Polyhedron::Facet_iterator it = P.facets_begin(); it != P.facets_end(); ++it, ++i)
{
it->id() = i;
}
// Ad hoc property_map to store normals. Face_index_map is used to
// map face_descriptors to a contiguous range of indices. See
// http://www.boost.org/libs/property_map/doc/vector_property_map.html
// for details.
boost::vector_property_map<Vector, Face_index_map>
normals(get(CGAL::face_index, P));
calculate_face_normals(
P // Graph
, get(CGAL::vertex_point, P) // map from vertex_descriptor to point
, normals // map from face_descriptor to Vector_3
);
std::cout << "Normals" << std::endl;
for(Polyhedron::Facet_iterator it = P.facets_begin(); it != P.facets_end(); ++it) {
// Facet_iterator is a face_descriptor, so we can use it as the
// key here
std::cout << normals[it] << std::endl;
}
return 0;
}