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

CGAL 4.8 - Triangulated Surface Mesh Simplification

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Surface_mesh_simplification/edge_collapse_enriched_polyhedron.cpp
#include <iostream>
#include <fstream>
#include <CGAL/Simple_cartesian.h>
#include <CGAL/Polyhedron_3.h>
#include <CGAL/IO/Polyhedron_iostream.h>
#include <CGAL/boost/graph/graph_traits_Polyhedron_3.h>
// Simplification function
#include <CGAL/Surface_mesh_simplification/edge_collapse.h>
// Visitor base
#include <CGAL/Surface_mesh_simplification/Edge_collapse_visitor_base.h>
// Extended polyhedron items which include an id() field
#include <CGAL/Polyhedron_items_with_id_3.h>
// Stop-condition policy
#include <CGAL/Surface_mesh_simplification/Policies/Edge_collapse/Count_ratio_stop_predicate.h>
// Non-default cost and placement policies
#include <CGAL/Surface_mesh_simplification/Policies/Edge_collapse/Midpoint_and_length.h>
typedef CGAL::Simple_cartesian<double> Kernel;
typedef Kernel::Point_3 Point ;
//
// Setup an enriched polyhedron type which stores an id() field in the items
//
typedef CGAL::Polyhedron_3<Kernel,CGAL::Polyhedron_items_with_id_3> Surface_mesh;
typedef Surface_mesh::Halfedge_handle Halfedge_handle ;
typedef Surface_mesh::Vertex_handle Vertex_handle ;
namespace SMS = CGAL::Surface_mesh_simplification ;
typedef SMS::Edge_profile<Surface_mesh> Profile ;
// The following is a Visitor that keeps track of the simplification process.
// In this example the progress is printed real-time and a few statistics are
// recorded (and printed in the end).
//
struct Stats
{
Stats()
: collected(0)
, processed(0)
, collapsed(0)
, non_collapsable(0)
, cost_uncomputable(0)
, placement_uncomputable(0)
{}
std::size_t collected ;
std::size_t processed ;
std::size_t collapsed ;
std::size_t non_collapsable ;
std::size_t cost_uncomputable ;
std::size_t placement_uncomputable ;
} ;
struct My_visitor : SMS::Edge_collapse_visitor_base<Surface_mesh>
{
My_visitor( Stats* s) : stats(s){}
// Called during the collecting phase for each edge collected.
void OnCollected( Profile const&, boost::optional<double> const& )
{
++ stats->collected ;
std::cerr << "\rEdges collected: " << stats->collected << std::flush ;
}
// Called during the processing phase for each edge selected.
// If cost is absent the edge won't be collapsed.
void OnSelected(Profile const&
,boost::optional<double> cost
,std::size_t initial
,std::size_t current
)
{
++ stats->processed ;
if ( !cost )
++ stats->cost_uncomputable ;
if ( current == initial )
std::cerr << "\n" << std::flush ;
std::cerr << "\r" << current << std::flush ;
}
// Called during the processing phase for each edge being collapsed.
// If placement is absent the edge is left uncollapsed.
void OnCollapsing(Profile const&
,boost::optional<Point> placement
)
{
if ( !placement )
++ stats->placement_uncomputable ;
}
// Called for each edge which failed the so called link-condition,
// that is, which cannot be collapsed because doing so would
// turn the surface mesh into a non-manifold.
void OnNonCollapsable( Profile const& )
{
++ stats->non_collapsable;
}
// Called AFTER each edge has been collapsed
void OnCollapsed( Profile const&, Vertex_handle )
{
++ stats->collapsed;
}
Stats* stats ;
} ;
int main( int argc, char** argv )
{
Surface_mesh surface_mesh;
std::ifstream is(argv[1]) ; is >> surface_mesh ;
// The items in this polyhedron have an "id()" field
// which the default index maps used in the algorithm
// need to get the index of a vertex/edge.
// However, the Polyhedron_3 class doesn't assign any value to
// this id(), so we must do it here:
int index = 0 ;
for( Surface_mesh::Halfedge_iterator eb = surface_mesh.halfedges_begin()
, ee = surface_mesh.halfedges_end()
; eb != ee
; ++ eb
)
eb->id() = index++;
index = 0 ;
for( Surface_mesh::Vertex_iterator vb = surface_mesh.vertices_begin()
, ve = surface_mesh.vertices_end()
; vb != ve
; ++ vb
)
vb->id() = index++;
// In this example, the simplification stops when the number of undirected edges
// drops below 10% of the initial count
SMS::Count_ratio_stop_predicate<Surface_mesh> stop(0.1);
Stats stats ;
My_visitor vis(&stats) ;
// The index maps are not explicitelty passed as in the previous
// example because the surface mesh items have a proper id() field.
// On the other hand, we pass here explicit cost and placement
// function which differ from the default policies, ommited in
// the previous example.
int r = SMS::edge_collapse
(surface_mesh
,stop
,CGAL::parameters::get_cost (SMS::Edge_length_cost <Surface_mesh>())
.get_placement(SMS::Midpoint_placement<Surface_mesh>())
.visitor (vis)
);
std::cout << "\nEdges collected: " << stats.collected
<< "\nEdges proccessed: " << stats.processed
<< "\nEdges collapsed: " << stats.collapsed
<< std::endl
<< "\nEdges not collapsed due to topological constraints: " << stats.non_collapsable
<< "\nEdge not collapsed due to cost computation constraints: " << stats.cost_uncomputable
<< "\nEdge not collapsed due to placement computation constraints: " << stats.placement_uncomputable
<< std::endl ;
std::cout << "\nFinished...\n" << r << " edges removed.\n"
<< (surface_mesh.size_of_halfedges()/2) << " final edges.\n" ;
std::ofstream os( argc > 2 ? argv[2] : "out.off" ) ; os << surface_mesh ;
return 0 ;
}
// EOF //