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//A method to construct a surface.
//Copyright (C) 2013 INRIA - Sophia Antipolis
//
//This program is free software: you can redistribute it and/or modify
//it under the terms of the GNU General Public License as published by
//the Free Software Foundation, either version 3 of the License, or
//(at your option) any later version.
//
//This program is distributed in the hope that it will be useful,
//but WITHOUT ANY WARRANTY; without even the implied warranty of
//MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
//GNU General Public License for more details.
//
//You should have received a copy of the GNU General Public License
//along with this program. If not, see <http://www.gnu.org/licenses/>.
//
// Author(s): Thijs van Lankveld
#ifndef SCALE_SPACE_SURFACE_CONSTRUCTER
#define SCALE_SPACE_SURFACE_CONSTRUCTER
#include <omp.h>
#include <iostream>
#include <list>
#include <map>
#include <vector>
#include <boost/iterator/transform_iterator.hpp>
#include <CGAL/utility.h>
#include <CGAL/Search_traits_3.h>
#include <CGAL/Orthogonal_incremental_neighbor_search.h>
#include <CGAL/Orthogonal_k_neighbor_search.h>
#include <CGAL/Random.h>
#include <CGAL/Delaunay_triangulation_3.h>
#include <CGAL/Triangulation_vertex_base_with_info_3.h>
#include <CGAL/Triangulation_cell_base_with_info_3.h>
#include <CGAL/Alpha_shape_3.h>
#include <CGAL/Alpha_shape_vertex_base_3.h>
#include <CGAL/Alpha_shape_cell_base_3.h>
#include <CGAL/Fixed_alpha_shape_3.h>
#include <CGAL/Fixed_alpha_shape_vertex_base_3.h>
#include <CGAL/Fixed_alpha_shape_cell_base_3.h>
#include <Eigen/Dense>
#include <CGAL/check3264.h>
namespace CGAL {
//a functor that returns a std::pair<Point,unsigned>.
//the unsigned integer is incremented at each call to
//operator()
template < class T >
class Auto_count: public std::unary_function< const T&, std::pair< T, unsigned int > > {
mutable unsigned int i;
public:
Auto_count(): i(0) {}
std::pair< T,unsigned int > operator()( const T& t ) const { return std::make_pair( t, i++ ); }
};
// Struct to choose between the alpha-shape and fixed alpha-shape
template < class Kernel, class Fixed_shape >
class _Shape {
typedef typename Kernel::FT Scalar;
typedef CGAL::Alpha_shape_vertex_base_3< Kernel,
CGAL::Triangulation_vertex_base_with_info_3< unsigned int, Kernel > > Vb;
typedef CGAL::Alpha_shape_cell_base_3< Kernel,
CGAL::Triangulation_cell_base_with_info_3< unsigned int, Kernel > > Cb;
typedef CGAL::Triangulation_data_structure_3<Vb,Cb> Tds;
public:
typedef CGAL::Delaunay_triangulation_3< Kernel, Tds > Structure;
typedef CGAL::Alpha_shape_3< Structure > Shape;
_Shape() {}
Shape* construct( Shape* shape, const Scalar& squared_radius ) {
if( shape ) return new Shape( *shape, squared_radius, Shape::GENERAL );
else return new Shape( squared_radius, Shape::GENERAL );
}
template < class InputIterator >
Shape* construct( InputIterator start, InputIterator end, const Scalar& squared_radius ) {
return new Shape( boost::make_transform_iterator( start, Auto_count<Point>() ),
boost::make_transform_iterator( end, Auto_count<Point>() ),
squared_radius, Shape::GENERAL );
}
}; // class _Shape
// Struct to choose between the alpha-shape and fixed alpha-shape
// specialization: fixed..
template < class Kernel >
class _Shape < Kernel, CGAL::Tag_true > {
typedef typename Kernel::FT Scalar;
typedef CGAL::Fixed_alpha_shape_vertex_base_3< Kernel,
CGAL::Triangulation_vertex_base_with_info_3< unsigned int, Kernel > > Vb;
typedef CGAL::Fixed_alpha_shape_cell_base_3< Kernel,
CGAL::Triangulation_cell_base_with_info_3< unsigned int, Kernel > > Cb;
typedef CGAL::Triangulation_data_structure_3<Vb,Cb> Tds;
public:
typedef CGAL::Delaunay_triangulation_3< Kernel, Tds > Structure;
typedef CGAL::Fixed_alpha_shape_3< Structure > Shape;
_Shape() {}
Shape* construct( Shape* shape, const Scalar& squared_radius ) {
if( shape ) return new Shape( *shape, squared_radius );
else return new Shape( squared_radius );
}
template < class InputIterator >
Shape* construct( InputIterator start, InputIterator end, const Scalar& squared_radius ) {
return new Shape( boost::make_transform_iterator( start, Auto_count<Point>() ),
boost::make_transform_iterator( end, Auto_count<Point>() ),
squared_radius );
}
}; // class _Shape
/// Compute a smoothed surface mesh from a collection of points.
/** An appropriate neighborhood size is estimated, followed by a
* number of smoothing iterations. Finally, the surface of the
* smoothed point set is computed.
*
* The order of the point set remains the same, meaning that
* the smoothed surface can be transposed back to its unsmoothed
* version by overwriting the smoothed point collection with its
* unsmoothed version.
* \tparam Kernel the geometric traits class. This class
* specifies, amongst other things, the number types and
* predicates used.
* \tparam Fixed_shape indicates whether shape of the object
* should be constructed for a fixed neighborhood size.
*
* Generally, constructing for a fixed neighborhood size is more
* efficient. This is not the case if the surface should be
* constructed for different neighborhood sizes without changing
* the point set or recomputing the scale-space.
* \tparam Shells indicates whether to collect the surface per shell.
*
* A shell is a connected component of the surface where connected
* facets are locally oriented towards the same side of the surface.
* \sa Mean_neighborhood_ball.
* \sa Scale_space_transform.
* \sa Surface_mesher.
*/
template < class Kernel, class Fixed_shape = CGAL::Tag_true, class Shells = CGAL::Tag_true >
class Scale_space_surface_reconstructer_3 {
// Searching for neighbors.
typedef typename CGAL::Search_traits_3< Kernel > Search_traits;
typedef typename CGAL::Orthogonal_k_neighbor_search< Search_traits >
Static_search;
typedef typename CGAL::Orthogonal_incremental_neighbor_search< Search_traits >
Dynamic_search;
typedef typename Dynamic_search::Tree Search_tree;
typedef CGAL::Random Random;
// Constructing the surface.
typedef _Shape< Kernel, Fixed_shape > Shape_generator;
typedef typename Shape_generator::Shape Shape;
typedef typename Shape::Vertex_handle Vertex_handle;
typedef typename Shape::Cell_handle Cell_handle;
typedef typename Shape::Facet Facet;
typedef typename Shape::All_cells_iterator All_cells_iterator;
typedef typename Shape::Finite_facets_iterator Finite_facets_iterator;
typedef typename Shape::Classification_type Classification_type;
public:
typedef Shells Collect_per_shell; ///< Whether to collect the surface per shell.
typedef typename Kernel::FT Scalar; ///< The number type.
typedef typename Kernel::Point_3 Point; ///< The point type.
typedef typename Kernel::Triangle_3 Triangle; ///< The triangle type.
typedef Triple< unsigned int, unsigned int, unsigned int >
Triple; ///< A triangle of the surface.
typedef std::list< Triple > Tripleset; ///< A collection of triples.
typedef typename Search_tree::iterator Point_iterator; ///< An iterator over the points.
typedef typename Search_tree::const_iterator Point_const_iterator; ///< A constant iterator over the points.
private:
typedef typename std::vector<Point> Pointset; ///< A collection of points.
private:
Search_tree _tree; // To quickly search for nearest neighbors.
Random _generator; // For sampling random points.
unsigned int _mean_neighbors; // The number of nearest neighbors in the mean neighborhood.
unsigned int _samples; // The number of sample points for estimating the mean neighborhood.
Scalar _squared_radius; // The squared mean neighborhood radius.
// The shape must be a pointer, because the alpha of
// a Fixed_alpha_shape_3 can only be set at
// construction and its assignment operator is private.
Shape* _shape;
// The surface. If the surface is collected per shell,
// consecutive triples belong to the same shell and
// different shells are separated by a (0,0,0) triple.
Tripleset _surface;
private:
void clear_tree() { _tree.clear(); }
public:
/// Default constructor.
/** \param sq_radius the squared radius of the
* neighborhood size. If this value is negative when
* the point set is smoothed or when the surface is computed,
* the neighborhood size will be computed automatically.
*/
Scale_space_surface_reconstructer_3(unsigned int neighbors = 30, unsigned int samples = 200, Scalar sq_radius = -1 ): _mean_neighbors(neighbors), _samples(samples), _squared_radius( sq_radius ), _shape(0) {}
~Scale_space_surface_reconstructer_3() { deinit_shape(); }
private:
void deinit_shape() { if( _shape != 0 ) { delete _shape; _shape = 0; } }
public:
Point_iterator scale_space_begin() { return _tree.begin(); }
Point_iterator scale_space_end() { return _tree.end(); }
Point_const_iterator scale_space_begin() const { return _tree.begin(); }
Point_const_iterator scale_space_end() const { return _tree.begin(); }
bool has_surface() const { return _shape != 0; }
void clear_surface() {
if( has_surface() ) {
_shape->clear();
}
}
/// Insert a collection of points.
/** \tparam InputIterator an iterator over a collection of points.
* The iterator must point to a Point type.
* \param start an iterator to the first point of the collection.
* \param end a past-the-end iterator for the point collection.
* \sa compute_surface(InputIterator start, InputIterator end).
*/
template < class InputIterator >
void insert_points( InputIterator start, InputIterator end ) {
_tree.insert( start, end );
}
void clear() {
clear_tree();
clear_surface();
}
/// Estimate the mean neighborhood size based on a number of sample points.
/** A neighborhood size is expressed as the radius of the smallest
* ball centered on a point such that the ball contains at least
* a specified number of points.
*
* The mean neighborhood size is then the mean of these radii,
* taken over a number of point samples.
* \return the estimated mean neighborhood size.
* \sa handlePoint(const Point& p).
* \sa operator()(InputIterator start, InputIterator end).
*/
Scalar estimate_mean_neighborhood( unsigned int neighbors = 30, unsigned int samples = 200 ) {
Kernel::Compute_squared_distance_3 squared_distance = Kernel().compute_squared_distance_3_object();
_mean_neighbors = neighbors;
_samples = samples;
unsigned int handled = 0;
unsigned int checked = 0;
Scalar radius = 0;
if( !_tree.is_built() )
_tree.build();
for (typename Search_tree::const_iterator it = _tree.begin(); it != _tree.end(); ++it) {
if (samples >= (_tree.size() - handled) || _generator.get_double() < double(samples - checked) / (_tree.size() - handled)) {
// The neighborhood should contain the point itself as well.
Static_search search( _tree, *it, _mean_neighbors+1 );
radius += CGAL::sqrt( CGAL::to_double( squared_distance( *it, ( search.end()-1 )->first ) ) );
++checked;
}
++handled;
}
radius /= double(checked);
set_mean_neighborhood( radius );
return radius;
}
template < class InputIterator >
Scalar estimate_mean_neighborhood(InputIterator start, InputIterator end, unsigned int neighbors = 30, unsigned int samples = 200) {
insert_points(start, end);
return estimate_mean_neighborhood(neighbors, samples);
}
// -1 if not yet set.
Scalar get_squared_mean_neighborhood() const { return _squared_radius; }
void set_mean_neighborhood( const Scalar& radius ) {
_squared_radius = radius * radius;
if( has_surface() )
_shape = Shape_generator().construct( _shape, _squared_radius );
}
bool has_squared_mean_neighborhood() const {
return sign( _squared_radius ) == POSITIVE;
}
unsigned int get_mean_neighbors() const { return _mean_neighbors; }
unsigned int get_number_samples() const { return _samples; }
void set_mean_neighbors(unsigned int neighbors) { _mean_neighbors = neighbors;}
void set_number_samples(unsigned int samples) { _samples = samples; }
/// Compute a number of iterations of scale-space transforming.
/** If earlier iterations have been computed, calling smooth_scale_space()
* will add more iterations.
*
* If the mean neighborhood is negative, it will be computed first.
* \param iterations the number of iterations to perform.
*/
void smooth_scale_space(unsigned int iterations = 1) {
typedef std::vector<unsigned int> CountVec;
typedef typename std::map<Point, size_t> PIMap;
typedef Eigen::Matrix<double, 3, Eigen::Dynamic> Matrix3D;
typedef Eigen::Array<double, 1, Eigen::Dynamic> Array1D;
typedef Eigen::Matrix3d Matrix3;
typedef Eigen::Vector3d Vector3;
typedef Eigen::SelfAdjointEigenSolver<Matrix3> EigenSolver;
typedef _ENV::s_ptr_type p_size_t;
// This method must be called after filling the point collection.
CGAL_assertion(!_tree.empty());
if( !has_squared_mean_neighborhood() )
estimate_mean_neighborhood( _mean_neighbors, _samples );
Pointset smoothed_points;
smoothed_points.assign( _tree.begin(), _tree.end() );
_tree.clear();
// Construct a search tree of the points.
// Note that the tree has to be local for openMP.
for (unsigned int iter = 0; iter < iterations; ++iter) {
Search_tree tree( smoothed_points.begin(), smoothed_points.end() );
if(!tree.is_built())
tree.build();
// Collect the number of neighbors of each point.
// This can be done parallel.
CountVec neighbors(_tree.size(), 0);
Kernel::Compare_squared_distance_3 compare;
p_size_t count = _tree.size(); // openMP can only use signed variables.
const Scalar squared_radius = _squared_radius; // openMP can only use local variables.
#pragma omp parallel for shared(count,tree,smoothed_points,squared_radius,neighbors) firstprivate(compare)
for (p_size_t i = 0; i < count; ++i) {
// Iterate over the neighbors until the first one is found that is too far.
Dynamic_search search(tree, tree[i]);
for (Dynamic_search::iterator nit = search.begin(); nit != search.end() && compare(tree[i], nit->first, squared_radius) != CGAL::LARGER; ++nit)
++neighbors[i];
}
// Construct a mapping from each point to its index.
PIMap indices;
p_size_t index = 0;
for( Search_tree::const_iterator tit = tree.begin(); tit != tree.end(); ++tit, ++index)
indices[ *tit ] = index;
// Compute the tranformed point locations.
// This can be done parallel.
#pragma omp parallel for shared(count,neighbors,tree,squared_radius) firstprivate(compare)
for (p_size_t i = 0; i < count; ++i) {
// If the neighborhood is too small, the vertex is not moved.
if (neighbors[i] < 4)
continue;
// Collect the vertices within the ball and their weights.
Dynamic_search search(tree, tree[i]);
Matrix3D pts(3, neighbors[i]);
Array1D wts(1, neighbors[i]);
int column = 0;
for (Dynamic_search::iterator nit = search.begin(); nit != search.end() && compare(tree[i], nit->first, squared_radius) != CGAL::LARGER; ++nit, ++column) {
pts(0, column) = CGAL::to_double(nit->first[0]);
pts(1, column) = CGAL::to_double(nit->first[1]);
pts(2, column) = CGAL::to_double(nit->first[2]);
wts(column) = 1.0 / neighbors[indices[nit->first]];
}
// Construct the barycenter.
Vector3 bary = (pts.array().rowwise() * wts).rowwise().sum() / wts.sum();
// Replace the points by their difference with the barycenter.
pts = (pts.colwise() - bary).array().rowwise() * wts;
// Construct the weighted covariance matrix.
Matrix3 covariance = Matrix3::Zero();
for (column = 0; column < pts.cols(); ++column)
covariance += wts.matrix()(column) * pts.col(column) * pts.col(column).transpose();
// Construct the Eigen system.
EigenSolver solver(covariance);
// If the Eigen system does not converge, the vertex is not moved.
if (solver.info() != Eigen::Success)
continue;
// Find the Eigen vector with the smallest Eigen value.
std::ptrdiff_t index;
solver.eigenvalues().minCoeff(&index);
if (solver.eigenvectors().col(index).imag() != Vector3::Zero()) {
// This should actually never happen!
CGAL_assertion(false);
continue;
}
Vector3 n = solver.eigenvectors().col(index).real();
// The vertex is moved by projecting it onto the plane
// through the barycenter and orthogonal to the Eigen vector with smallest Eigen value.
Vector3 bv = Vector3(CGAL::to_double(tree[i][0]), CGAL::to_double(tree[i][1]), CGAL::to_double(tree[i][2])) - bary;
Vector3 per = bary + bv - (n.dot(bv) * n);
smoothed_points[i] = Point(per(0), per(1), per(2));
}
}
_tree.insert( smoothed_points.begin(), smoothed_points.end() );
}
/// Compute a number of transform iterations on a collection of points.
/** This method is equivalent to running [insert_points(start, end)](\ref insert_points)
* followed by [smooth_scale_space(iterations)](\ref smooth_scale_space).
* \tparam InputIterator an iterator over a collection of points.
* The iterator must point to a Point type.
* \param start an iterator to the first point of the collection.
* \param end a past-the-end iterator for the point collection.
* \param iterations the number of iterations to perform.
* \sa operator()(InputIterator start, InputIterator end).
* \sa assign(InputIterator start, InputIterator end).
* \sa iterate(unsigned int iterations).
*/
template < class InputIterator >
void smooth_scale_space(InputIterator start, InputIterator end, unsigned int iterations = 1) {
insert_points(start, end);
smooth_scale_space(iterations);
}
private:
// Once a facet is added to the surface, it is marked as handled.
inline bool is_handled( Cell_handle c, unsigned int li ) const {
switch( li ) {
case 0: return ( c->info()&1 ) != 0;
case 1: return ( c->info()&2 ) != 0;
case 2: return ( c->info()&4 ) != 0;
case 3: return ( c->info()&8 ) != 0;
}
return false;
}
inline bool is_handled( const Facet& f ) const { return is_handled( f.first, f.second ); }
inline void set_handled( Cell_handle c, unsigned int li ) {
switch( li ) {
case 0: c->info() |= 1; return;
case 1: c->info() |= 2; return;
case 2: c->info() |= 4; return;
case 3: c->info() |= 8; return;
}
}
inline void set_handled( Facet f ) { set_handled( f.first, f.second ); }
public:
// make new construct_shape() method for when pts already known...
void construct_shape() {
construct_shape( scale_space_begin(), scale_space_end() );
}
/*// For if you already have a Delaunay triangulation of the points.
void construct_shape(Shape_generator::Structure& tr ) {
deinit_shape();
if( !has_squared_mean_neighborhood() )
estimate_mean_neighborhood( _mean_neighbors, _samples );
_shape = Shape_generator().construct( *tr, r2 );
}*/
// If you don't want to smooth the point set.
template < class InputIterator >
void construct_shape(InputIterator start, InputIterator end) {
deinit_shape();
if( !has_squared_mean_neighborhood() )
estimate_mean_neighborhood( _mean_neighbors, _samples );
_shape = Shape_generator().construct( start, end, _squared_radius );
}
private:
Triple ordered_facet_indices( const Facet& f ) const {
if( (f.second&1) == 0 )
return Triple( f.first->vertex( (f.second+2)&3 )->info(),
f.first->vertex( (f.second+1)&3 )->info(),
f.first->vertex( (f.second+3)&3 )->info() );
else
return Triple( f.first->vertex( (f.second+1)&3 )->info(),
f.first->vertex( (f.second+2)&3 )->info(),
f.first->vertex( (f.second+3)&3 )->info() );
}
void collect_shell( Cell_handle c, unsigned int li ) {
// Collect one surface mesh from the alpha-shape in a fashion similar to ball-pivoting.
// Invariant: the facet is regular or singular.
// To stop stack overflows: use own stack.
std::stack<Facet> stack;
stack.push( Facet(c, li) );
Facet f;
Cell_handle n, p;
int ni, pi;
Vertex_handle a;
Classification_type cl;
bool processed = false;
while( !stack.empty() ) {
f = stack.top();
stack.pop();
// Check if the cell was already handled.
// Note that this is an extra check that in many cases is not necessary.
if( is_handled(f) )
continue;
// The facet is part of the surface.
CGAL_triangulation_assertion( !_shape->is_infinite(f) );
set_handled(f);
// Output the facet as a triple of indices.
_surface.push_back( ordered_facet_indices(f) );
if( Shells::value ) {
// Pivot over each of the facet's edges and continue the surface at the next regular or singular facet.
for( unsigned int i = 0; i < 4; ++i ) {
// Skip the current facet.
if( i == f.second || is_handled(f.first, i) )
continue;
// Rotate around the edge (starting from the shared facet in the current cell) until a regular or singular facet is found.
n = f.first;
ni = i;
a = f.first->vertex(f.second);
cl = _shape->classify( Facet(n, ni) );
while( cl != Shape::REGULAR && cl != Shape::SINGULAR ) {
p = n;
n = n->neighbor(ni);
ni = n->index(a);
pi = n->index(p);
a = n->vertex(pi);
cl = _shape->classify( Facet(n, ni) );
}
// Continue the surface at the next regular or singular facet.
stack.push( Facet(n, ni) );
}
processed = true;
}
}
// We indicate the end of a shell by the (0,0,0) triple.
if( Shells::value && processed )
_surface.push_back( Triple(0,0,0) );
}
void collect_shell( const Facet& f ) {
collect_shell( f.first, f.second );
}
public:
template < class OutputIterator >
OutputIterator collect_surface( OutputIterator out ) {
if( !has_squared_mean_neighborhood() )
estimate_mean_neighborhood( _mean_neighbors, _samples );
// Collect all surface meshes from the alpha-shape in a fashion similar to ball-pivoting.
// Reset the facet handled markers.
for( All_cells_iterator cit = _shape->all_cells_begin(); cit != _shape->all_cells_end(); ++cit )
cit->info() = 0;
// We check each of the facets: if it is not handled and either regular or singular,
// we start collecting the next surface from here.
Facet m;
int ns = 0;
for( Finite_facets_iterator fit = _shape->finite_facets_begin(); fit != _shape->finite_facets_end(); ++fit ) {
m = _shape->mirror_facet( *fit );
switch( _shape->classify( *fit ) ) {
case Shape::REGULAR:
if( !is_handled(*fit) && !is_handled(m) )
++ns;
// Build a surface from the outer cell.
if( _shape->classify(fit->first) == Shape::EXTERIOR )
collect_shell( *fit );
else
collect_shell( m );
break;
case Shape::SINGULAR:
if( !is_handled( *fit ) )
++ns;
// Build a surface from both incident cells.
collect_shell( *fit );
if( !is_handled(m) )
++ns;
collect_shell( m );
break;
}
}
return out;
}
template < class InputIterator, class OutputIterator >
OutputIterator collect_surface( InputIterator start, InputIterator end, OutputIterator out ) {
construct_shape( start, end );
return collect_surface( out );
}
template < class InputIterator >
void collect_surface( InputIterator start, InputIterator end ) {
construct_shape( start, end );
collect_surface( std::back_inserter(_surface) );
}
void collect_surface() {
collect_surface( scale_space_begin(), scale_space_end() );
}
const Tripleset& surface() const { return _surface; }
Tripleset& surface() { return _surface; }
/// Compute a smoothed surface mesh from a collection of points.
/** This is equivalent to calling insert_points(),
* iterate(), and compute_surface().
*
* After this computation, the surface can be accessed using
* surface().
* \tparam InputIterator an iterator over the point collection.
* The iterator must point to a Point type.
* \param start an iterator to the first point of the collection.
* \param end a past-the-end iterator for the point collection.
*
* \sa surface().
* \sa surface() const.
*/
template < class InputIterator >
void compute_surface(InputIterator start, InputIterator end, unsigned int neighbors = 30, unsigned int iterations = 4, unsigned int samples = 200) {
typedef std::map<Point, unsigned int> Map;
// Compute the radius for which the mean ball would contain the required number of neighbors.
clear();
insert_points( start, end );
_mean_neighbors = neighbors;
_samples = samples;
if( !has_squared_mean_neighborhood() )
estimate_mean_neighborhood( _mean_neighbors, samples ); // TMP: move this into transform() and compute_surface()
// Smooth the scale space.
smooth_scale_space(iterations);
// Mesh the perturbed points.
collect_surface();
}
}; // class Scale_space_surface_reconstructer_3
template< typename T1, typename T2, typename T3 >
std::ostream&
operator<<( std::ostream& os, const Triple< T1, T2, T3 >& t ) {
return os << t.first << " " << t.second << " " << t.third;
}
template< typename T1, typename T2, typename T3 >
std::istream&
operator>>( std::istream& is, Triple< T1, T2, T3 >& t ) {
return is >> t.first >> t.second >> t.third;
}
} // namespace CGAL
#endif // SCALE_SPACE_SURFACE_CONSTRUCTER