NOTE: See edit at the bottom of this post for code that solves my problem.
I am constructing a Voronoi diagram in CGAL. Each site in my diagram has some non-geometric information associated with it (like the population of a city, or the temperature at a certain location). After I construct the Voronoi diagram, I will perform location queries on it, and I will need to be able to recover this non-geometric information from the query results. It seems that CGAL has the capability to do this; this is discussed for example here in the context of Delaunay triangulations. But I cannot figure out how to apply this technique for Voronoi diagrams. Here's what I tried, which fails to compile:
Broken code removed. See working code example below.
Remainder of question deleted, since it pertains to deleted, broken code. See working code example below.
EDIT 1: Fixed errors pointed pointed out by sloriot, and included complete compiler output.
EDIT 2: In a comment, Dr. Fabri suggested that I start by modifying the CGAL example vd_2_point_location.cpp. Following his advice, I here post a working code. This is a very lightly modified version of vd_2_point_location.cpp.
// standard includes
#include <iostream>
#include <fstream>
#include <cassert>
// includes for defining the Voronoi diagram adaptor
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Delaunay_triangulation_2.h>
#include <CGAL/Triangulation_vertex_base_with_info_2.h>
#include <CGAL/Voronoi_diagram_2.h>
#include <CGAL/Delaunay_triangulation_adaptation_traits_2.h>
#include <CGAL/Delaunay_triangulation_adaptation_policies_2.h>
// typedefs for defining the adaptor
typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Triangulation_vertex_base_with_info_2<int, K> VB;
typedef CGAL::Triangulation_data_structure_2<VB> TDS;
typedef CGAL::Delaunay_triangulation_2<K,TDS> DT;
typedef CGAL::Delaunay_triangulation_adaptation_traits_2<DT> AT;
typedef CGAL::Delaunay_triangulation_caching_degeneracy_removal_policy_2<DT> AP;
typedef CGAL::Voronoi_diagram_2<DT,AT,AP> VD;
// typedef for the result type of the point location
typedef AT::Site_2 Site_2;
typedef AT::Point_2 Point_2;
typedef VD::Locate_result Locate_result;
typedef VD::Vertex_handle Vertex_handle;
typedef VD::Face_handle Face_handle;
typedef VD::Halfedge_handle Halfedge_handle;
typedef VD::Ccb_halfedge_circulator Ccb_halfedge_circulator;
void print_endpoint(Halfedge_handle e, bool is_src) {
std::cout << "\t";
if ( is_src ) {
if ( e->has_source() ) std::cout << e->source()->point() << std::endl;
else std::cout << "point at infinity" << std::endl;
} else {
if ( e->has_target() ) std::cout << e->target()->point() << std::endl;
else std::cout << "point at infinity" << std::endl;
}
}
int main()
{
std::ifstream ifs("data/data1.dt.cin");
assert( ifs );
VD vd;
Site_2 t;
int ctr=0;
while ( ifs >> t ) {
Face_handle fh = vd.insert(t); // Add the site...
fh->dual()->info() = ctr++; // ...attach some info to it
}
ifs.close();
assert( vd.is_valid() );
std::ifstream ifq("data/queries1.dt.cin");
assert( ifq );
Point_2 p;
while ( ifq >> p ) {
std::cout << "Query point (" << p.x() << "," << p.y()
<< ") lies on a Voronoi " << std::flush;
Locate_result lr = vd.locate(p);
if ( Vertex_handle* v = boost::get<Vertex_handle>(&lr) ) {
std::cout << "vertex." << std::endl;
std::cout << "The Voronoi vertex is:" << std::endl;
std::cout << "\t" << (*v)->point() << std::endl;
} else if ( Halfedge_handle* e = boost::get<Halfedge_handle>(&lr) ) {
std::cout << "edge." << std::endl;
std::cout << "The source and target vertices "
<< "of the Voronoi edge are:" << std::endl;
print_endpoint(*e, true);
print_endpoint(*e, false);
} else if ( Face_handle* f = boost::get<Face_handle>(&lr) ) {
std::cout << "face." << std::endl;
std::cout << "The info associated with this face is "
<< (*f)->dual()->info() << std::endl;
std::cout << "The vertices of the Voronoi face are"
<< " (in counterclockwise order):" << std::endl;
Ccb_halfedge_circulator ec_start = (*f)->ccb();
Ccb_halfedge_circulator ec = ec_start;
do {
print_endpoint(ec, false);
} while ( ++ec != ec_start );
}
std::cout << std::endl;
}
ifq.close();
return 0;
}
Related
I'm using CGAL (v. 4.14-2) to compute the visibility region (polygon) within a simple polygon from one of its vertices, using the Simple_polygon_visibility_2 class.
On a particular combination of polygon/vertex, I'm getting the following assertion error:
terminate called after throwing an instance of 'CGAL::Assertion_exception'
what(): CGAL ERROR: assertion violation!
Expr: k+1<vertices.size()
File: /usr/include/CGAL/Simple_polygon_visibility_2.h
Line: 678
This occurs in the method scan_edges of the class Simple_polygon_visibility_2, it seems like there should be some intersection with the given segment/ray, but none was found.
When I run the same code with the class Triangular_expansion_visibility_2, it seems to work, giving the output:
Regularized visibility region of q has 8 edges:
[7968 492 -> 7938 428]
[7884 408 -> 7968 492]
[8040 428 -> 7884 408]
[8090.99 428 -> 8040 428]
[8105.55 458.865 -> 8090.99 428]
[8090 456 -> 8105.55 458.865]
[7968 446 -> 8090 456]
[7938 428 -> 7968 446]
Here's a minimal working example:
#include <CGAL/Arr_naive_point_location.h>
#include <CGAL/Arr_segment_traits_2.h>
#include <CGAL/Arrangement_2.h>
#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Polygon_2.h>
#include <CGAL/Simple_polygon_visibility_2.h>
#include <CGAL/Triangular_expansion_visibility_2.h>
#include <fstream>
#include <iostream>
#include <string>
#include <list>
#include <vector>
typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
typedef Kernel::Point_2 Point_2;
typedef Kernel::Segment_2 Segment_2;
typedef CGAL::Polygon_2<Kernel, std::list<Point_2>> Polygon_2;
typedef CGAL::Arr_segment_traits_2<Kernel> Traits_2;
typedef CGAL::Arrangement_2<Traits_2> Arrangement_2;
typedef Arrangement_2::Face_handle Face_handle;
typedef Arrangement_2::Vertex_handle ArrVertex_handle;
typedef Arrangement_2::Edge_const_iterator Edge_const_iterator;
typedef Arrangement_2::Ccb_halfedge_circulator Ccb_halfedge_circulator;
using namespace std;
vector<Point_2> readInput() {
vector<Point_2> Points;
ifstream File;
File.open("polygon");
string Line;
long int Idx, XCoord, YCoord;
while (getline(File, Line)) {
istringstream Iss(Line);
Iss >> Idx >> XCoord >> YCoord;
Points.push_back({XCoord, YCoord});
}
return Points;
}
int main() {
// create environment
std::vector<Segment_2> segments;
Arrangement_2 env;
Segment_2 CurrSegment;
Polygon_2 AuxPoly;
auto Points = readInput();
auto QueryPt = Points[0];
ArrVertex_handle CurrPtHandle =
env.insert_in_face_interior(QueryPt, env.unbounded_face());
AuxPoly.push_back(Points[0]);
ArrVertex_handle NextPtHandle = CurrPtHandle;
ArrVertex_handle QueryPtHandle = CurrPtHandle;
for (auto i = 1; i < Points.size(); ++i) {
NextPtHandle = env.insert_in_face_interior(Points[i], env.unbounded_face());
CurrSegment = Segment_2(CurrPtHandle->point(), NextPtHandle->point());
env.insert_at_vertices(CurrSegment, CurrPtHandle, NextPtHandle);
CurrPtHandle = NextPtHandle;
AuxPoly.push_back(Points[i]);
}
assert(AuxPoly.is_simple());
CurrSegment = Segment_2(CurrPtHandle->point(), QueryPtHandle->point());
auto HalfEHandle =
env.insert_at_vertices(CurrSegment, CurrPtHandle, QueryPtHandle);
if (HalfEHandle->face()->is_unbounded()) {
// there are exactly two incident halfedges in the query point
auto FirstHalfE = HalfEHandle->target()->incident_halfedges();
HalfEHandle = (FirstHalfE != HalfEHandle) ? FirstHalfE : next(FirstHalfE, 1);
}
// compute non regularized visibility area
// Define visibiliy object type that computes regularized visibility area
typedef CGAL::Simple_polygon_visibility_2<Arrangement_2, CGAL::Tag_true> RSPV;
// typedef CGAL::Triangular_expansion_visibility_2<Arrangement_2, CGAL::Tag_true> RSPV;
Arrangement_2 regular_output;
RSPV regular_visibility(env);
regular_visibility.compute_visibility(QueryPtHandle->point(), HalfEHandle, regular_output);
std::cout << "Regularized visibility region of q has "
<< regular_output.number_of_edges() << " edges:" << std::endl;
for (Edge_const_iterator eit = regular_output.edges_begin();
eit != regular_output.edges_end(); ++eit)
std::cout << "[" << eit->source()->point() << " -> "
<< eit->target()->point() << "]" << std::endl;
return 0;
}
an auxiliary file arr_print.h to print the arrangement:
#ifndef _PRINT_ARR_H_
#define _PRINT_ARR_H_
#include <iostream>
//-----------------------------------------------------------------------------
// Print all neighboring vertices to a given arrangement vertex.
//
template<class Arrangement>
void print_neighboring_vertices (typename Arrangement::Vertex_const_handle v)
{
if (v->is_isolated())
{
std::cout << "The vertex (" << v->point() << ") is isolated" << std::endl;
return;
}
typename Arrangement::Halfedge_around_vertex_const_circulator first, curr;
typename Arrangement::Vertex_const_handle u;
std::cout << "The neighbors of the vertex (" << v->point() << ") are:";
first = curr = v->incident_halfedges();
do
{
// Note that the current halfedge is (u -> v):
u = curr->source();
std::cout << " (" << u->point() << ")";
++curr;
} while (curr != first);
std::cout << std::endl;
return;
}
//-----------------------------------------------------------------------------
// Print all vertices (points) and edges (curves) along a connected component
// boundary.
//
template<class Arrangement>
void print_ccb (typename Arrangement::Ccb_halfedge_const_circulator circ)
{
typename Arrangement::Ccb_halfedge_const_circulator curr = circ;
typename Arrangement::Halfedge_const_handle he;
std::cout << "(" << curr->source()->point() << ")";
do
{
he = curr;
std::cout << " [" << he->curve() << "] "
<< "(" << he->target()->point() << ")";
++curr;
} while (curr != circ);
std::cout << std::endl;
return;
}
//-----------------------------------------------------------------------------
// Print the boundary description of an arrangement face.
//
template<class Arrangement>
void print_face (typename Arrangement::Face_const_handle f)
{
// Print the outer boundary.
if (f->is_unbounded())
{
std::cout << "Unbounded face. " << std::endl;
}
else
{
std::cout << "Outer boundary: ";
print_ccb<Arrangement> (f->outer_ccb());
}
// Print the boundary of each of the holes.
typename Arrangement::Hole_const_iterator hole;
int index = 1;
for (hole = f->holes_begin(); hole != f->holes_end(); ++hole, ++index)
{
std::cout << " Hole #" << index << ": ";
print_ccb<Arrangement> (*hole);
}
// Print the isolated vertices.
typename Arrangement::Isolated_vertex_const_iterator iv;
for (iv = f->isolated_vertices_begin(), index = 1;
iv != f->isolated_vertices_end(); ++iv, ++index)
{
std::cout << " Isolated vertex #" << index << ": "
<< "(" << iv->point() << ")" << std::endl;
}
return;
}
//-----------------------------------------------------------------------------
// Print the given arrangement.
//
template<class Arrangement>
void print_arrangement (const Arrangement& arr)
{
// CGAL_precondition (arr.is_valid());
// Print the arrangement vertices.
typename Arrangement::Vertex_const_iterator vit;
std::cout << arr.number_of_vertices() << " vertices:" << std::endl;
for (vit = arr.vertices_begin(); vit != arr.vertices_end(); ++vit)
{
std::cout << "(" << vit->point() << ")";
if (vit->is_isolated())
std::cout << " - Isolated." << std::endl;
else
std::cout << " - degree " << vit->degree() << std::endl;
}
// Print the arrangement edges.
typename Arrangement::Edge_const_iterator eit;
std::cout << arr.number_of_edges() << " edges:" << std::endl;
for (eit = arr.edges_begin(); eit != arr.edges_end(); ++eit)
std::cout << "[" << eit->curve() << "]" << std::endl;
// Print the arrangement faces.
typename Arrangement::Face_const_iterator fit;
std::cout << arr.number_of_faces() << " faces:" << std::endl;
for (fit = arr.faces_begin(); fit != arr.faces_end(); ++fit)
print_face<Arrangement> (fit);
return;
}
#endif
The input polygon:
input polygon
The input file has in each line the polygon vertex id, followed by its x- and-coordinates. The query point is the one with id 1716.
Could anyone help me with this issue?
Thank you all in advance.
I am given STL format 3D models coming out of Cinema 4D. My goal is to manipulate them using CGAL. For now, I am only trying to load the model as a Polyhedron_3 using the following code :
using namespace std;
typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
typedef CGAL::Polyhedron_3<Kernel> Polyhedron_3;
typedef CGAL::Simple_cartesian<double> K;
typedef K::Point_2 Point_2;
typedef K::Point_3 Point_3;
int main()
{
std::string stl_file_name;
cout << "opening file\n";
stl_file_name = "D:\\Julien\\Edit3D_I5_STImier.stl";
Polyhedron_3 poly_Partition;
std::ifstream stl_file(stl_file_name, std::ifstream::in);
std::vector<CGAL::cpp11::array<double, 3> > points;
std::vector<CGAL::cpp11::array<int, 3> > triangles;
cout << "reading file\n";
CGAL::read_STL(stl_file, points, triangles);
cout << "closing file \n";
stl_file.close();
cout << "processing mesh\n";
int spoints_nb = points.size();
cout << "number of points in soup : " << spoints_nb << "\n";
int poly_nb = triangles.size();
cout << "number of polys in soup : " << poly_nb << "\n";
CGAL::Polygon_mesh_processing::orient_polygon_soup(points, triangles);
CGAL::Polygon_mesh_processing::polygon_soup_to_polygon_mesh(points, triangles, poly_Partition);
int vertices_nb = poly_Partition.size_of_facets();
cout << "number of facets : " << vertices_nb << "\n";
int points_nb = points.size();
cout << "number of points : " << points_nb << "\n";
int triangles_nb = triangles.size();
cout << "number of triangles : " << triangles_nb << "\n";
std::vector<Point_3> points_3;
std::vector<CGAL::cpp11::array<double, 3>>::iterator it;
for (it = points.begin() ; it != points.end(); ++it) {
CGAL::cpp11::array<double, 3> a = *it;
Point_3 point = Point_3(a[0], a[1], a[2]);
points_3.push_back(point);
}
K::Iso_cuboid_3 c3 = CGAL::bounding_box(points_3.begin(), points_3.end());
for (int i = 0; i < 8; i++) {
Point_3 vert = c3.vertex(i);
cout << vert.hx() << ", " << vert.hy() << ", " << vert.hz() << "\n";
}
return 0;
}
Problem is I only get 19 points and 24 triangles. When I turn on verbose on read_STL I get many ignore degenerate face messages in console.
My question is : how do I make the faces NOT degenerate ? Is there a more forgiving (with respect to "degeneracy") way to read STL files ?
I am new to both C++ and CGAL so please forgive me if my code hurts your eyes.
Following this: How to print the faces of a Voronoi diagram?, I now have:
#include <iostream>
#include <fstream>
#include <cassert>
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Segment_Delaunay_graph_2.h>
#include <CGAL/Segment_Delaunay_graph_adaptation_policies_2.h>
#include <CGAL/Segment_Delaunay_graph_traits_2.h>
typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Segment_Delaunay_graph_traits_2<K> Gt;
typedef CGAL::Segment_Delaunay_graph_2<Gt> DT;
int main() {
std::ifstream ifs("data.cin");
assert( ifs );
DT vd;
DT::Site_2 site;
// read the sites from the stream and insert them in the diagram
while ( ifs >> site ) { vd.insert( site ); }
ifs.close();
// validate the diagram
assert( vd.is_valid(true, 1) );
std::cout << std::endl << std::endl;
// Iterate over edges
DT::Finite_edges_iterator eit = vd.finite_edges_begin();
for (int k = 1; eit != vd.finite_edges_end(); ++eit, ++k) {
DT::Edge e = *eit;
//std::cout << e << std::endl;
}
}
However, an edge cannot be printed that simply (with cout). How to do it?
Here is the error from another attempt:
/home/gsamaras/CGAL-4.7/code/DelaunayTOvoronoi/delTovor.cpp:30:27: error: ‘CGAL::Triangulation_ds_edge_iterator_2<CGAL::Triangulation_data_structure_2<CGAL::Segment_Delaunay_graph_vertex_base_2<CGAL::Segment_Delaunay_graph_storage_traits_2<CGAL::Segment_Delaunay_graph_traits_2<CGAL::Epick> >, CGAL::Triangulation_ds_vertex_base_2<void> >, CGAL::Segment_Delaunay_graph_face_base_2<CGAL::Segment_Delaunay_graph_traits_2<CGAL::Epick>, CGAL::Triangulation_ds_face_base_2<void> > >, true>::Edge’ has no member named ‘site’
std::cout << eit->site() << std::endl;
^
You can print the sites forming the edge like this:
for (int k = 1; eit != vd.finite_edges_end(); ++eit, ++k) {
DT::Edge e = *eit;
std::cout << "k = " << k << std::endl;
if ( vd.is_infinite(e.first->vertex( vd.ccw(e.second) )) )
std::cout << "infinite\n";
else
std::cout << e.first->vertex( vd.ccw(e.second) )->site() << std::endl;
if ( vd.is_infinite(e.first->vertex( vd.cw(e.second) )) )
std::cout << "infinite\n";
else
std::cout << e.first->vertex( vd.cw(e.second) )->site() << std::endl;
if ( vd.is_infinite(e.first->vertex( e.second )) )
std::cout << "infinite\n";
else
std::cout << e.first->vertex( e.second )->site() << std::endl;
if ( vd.is_infinite(vd.tds().mirror_vertex(e.first, e.second) ) )
std::cout << "infinite\n";
else
std::cout << vd.tds().mirror_vertex(e.first, e.second)->site() << std::endl;
}
I am trying to get a parametrized surface on a surface mesh (which is read from a STL format file.). I read some examples about parametrization provided by CGAL examples directory. I get to know that seam line should be provided in order to get a parametric surface on a arbitrary surface. But still I don't get how to make seam line. The below is my code so far. In summary, What I want to know is,
1) When CGAL::Parameterization_mesh_feature_extractor is used, how can I get vertices on the feature curves and make a seam line with the vertices?
2) Does CGAL provide a way to get intersection curve of a given surface and a cutting plane so that I can get a parametrized surface on a part of the given surface?
#include <cstdio>
#include <ctime>
#include <iostream>
#include <iomanip>
#include <algorithm>
#include <fstream>
#include <CGAL/IO/io.h>
#include <CGAL/IO/STL_reader.h>
#include <CGAL/Polyhedron_3.h>
#include <CGAL/Simple_cartesian.h>
#include <CGAL/polygon_soup_to_polyhedron_3.h>
#include <CGAL/Parameterization_polyhedron_adaptor_3.h>
#include <CGAL/Parameterization_mesh_patch_3.h>
#include <CGAL/parameterize.h>
int main(int argc, char* argv[]) {
clock_t time1, time2;
double read_time, write_time, build_time;
if(argc == 1) {
std::cout << "Please, give me a filename" << std::endl;
return 0;
}
std::ifstream infile(argv[1]);
if(infile.bad()) {
std::cout << "Infile not found or file corrupt" << std::endl;
return 1;
}
std::vector<CGAL::cpp11::array<double, 3> > points;
std::vector<CGAL::cpp11::array<int, 3> > triangles;
time1 = clock();
if (!CGAL::read_STL(infile, points, triangles)) {
std::cerr << "Error: invalid STL file" << std::endl;
return 0;
}
time2 = clock();
read_time = float(time2 - time1) / CLOCKS_PER_SEC;
fprintf(stdout, "Read time : %5.2f sec\n", read_time);
// Write polyhedron in Tecplot format
std::ofstream ofs("mesh.dat");
CGAL::set_ascii_mode(ofs);
time1 = clock();
ofs << "TITLE=\"\"" << std::endl;
ofs << "VARIABLES=\"X\" \"Y\" \"Z\"" << std::endl;
ofs << "ZONE T=\"None\" N=" << points.size() << " E=" << triangles.size() << " F=FEPOINT ET=TRIANGLE" << std::endl;
ofs.setf(std::ios::fixed);
ofs.precision(6);
for(std::vector<CGAL::cpp11::array<double, 3> >::iterator i = points.begin(); i != points.end(); ++i) {
ofs << (*i)[0] << " " << (*i)[1] << " " << (*i)[2] << std::endl;
}
for(std::vector<CGAL::cpp11::array<int, 3> >::iterator i = triangles.begin(); i != triangles.end(); ++i) {
ofs << (*i)[0]+1 << " " << (*i)[1]+1 << " " << (*i)[2]+1 << std::endl;
}
time2 = clock();
write_time = float(time2 - time1) / CLOCKS_PER_SEC;
fprintf(stdout, "Write time : %5.2f sec\n", write_time);
// build mesh
typedef CGAL::Simple_cartesian<double> Kernel;
typedef CGAL::Polyhedron_3<Kernel> Polyhedron;
Polyhedron mesh;
time1 = clock();
try{
// Try building a polyhedron
CGAL::polygon_soup_to_polyhedron_3(mesh, points, triangles);
if(! mesh.is_valid() || mesh.empty()){
std::cerr << "Error: Invalid polyhedron" << std::endl;
}
}
catch(...){}
time2 = clock();
build_time= float(time2 - time1) / CLOCKS_PER_SEC;
fprintf(stdout, "Build time : %5.2f sec\n", build_time);
// parameterization
typedef CGAL::Parameterization_polyhedron_adaptor_3<Polyhedron> Parameterization_polyhedron_adaptor;
// Type describing a border or seam as a vertex list
typedef std::list<Parameterization_polyhedron_adaptor::Vertex_handle> Seam;
//Create a second adaptor that virtually "cuts" the mesh following the 'seam' path
typedef CGAL::Parameterization_mesh_patch_3<Parameterization_polyhedron_adaptor> Mesh_patch_polyhedron;
Parameterization_polyhedron_adaptor mesh_adaptor(mesh);
////////////////////// cut graph ////////////////////////////////
typedef CGAL::Parameterization_mesh_feature_extractor<Parameterization_polyhedron_adaptor>
Mesh_feature_extractor;
Seam seam;
// Get reference to Polyhedron_3 mesh
Polyhedron& mesh_ref = mesh_adaptor.get_adapted_mesh();
// Extract mesh borders and compute genus
Mesh_feature_extractor feature_extractor(mesh_adaptor);
int nb_borders = feature_extractor.get_nb_borders();
int genus = feature_extractor.get_genus(); // genus means a hole inside a surface
std::cout << "# borders: " << nb_borders << " # holes: " << genus << std::endl;
std::cout << feature_extractor.get_borders()[0] << std::endl;
///////////////////// end of cut graph //////////////////////////
/*
Mesh_patch_polyhedron mesh_patch(mesh_adaptor, seam.begin(), seam.end());
if (!mesh_patch.is_valid())
{
std::cerr << "Input mesh not supported: non manifold shape or invalid cutting" << std::endl;
return EXIT_FAILURE;
}
typedef CGAL::Parameterizer_traits_3<Mesh_patch_polyhedron> Parameterizer; // Type that defines the error codes
Parameterizer::Error_code err = CGAL::parameterize(mesh_patch);
switch(err) {
case Parameterizer::OK: // Success
break;
case Parameterizer::ERROR_EMPTY_MESH: // Input mesh not supported
case Parameterizer::ERROR_NON_TRIANGULAR_MESH:
case Parameterizer::ERROR_NO_TOPOLOGICAL_DISC:
case Parameterizer::ERROR_BORDER_TOO_SHORT:
std::cerr << "Input mesh not supported: " << Parameterizer::get_error_message(err) << std::endl;
return EXIT_FAILURE;
break;
default: // Error
std::cerr << "Error: " << Parameterizer::get_error_message(err) << std::endl;
return EXIT_FAILURE;
break;
};
// Raw output: dump (u,v) pairs
Polyhedron::Vertex_const_iterator pVertex;
for (pVertex = mesh.vertices_begin(); pVertex != mesh.vertices_end(); pVertex++)
{
// (u,v) pair is stored in any halfedge
double u = mesh_adaptor.info(pVertex->halfedge())->uv().x();
double v = mesh_adaptor.info(pVertex->halfedge())->uv().y();
std::cout << "(u,v) = (" << u << "," << v << ")" << std::endl;
}
*/
return 0;
}
I have never used CGAL and have got almost no C/C++ experience. But following
Google I have however managed to compile the example "Alpha_shapes_3"
(\CGAL-4.1-beta1\examples\Alpha_shapes_3) on a Windows 7 64bit machine using
visual studio 2010.
Now if we check the source code for the program "ex_alpha_shapes_3" we
notice that a data file called "bunny_1000" is red where the 3d point
cluster resides.
Now my question is how can I change the source code so that after the alpha
shape is computed for the given points, surface mesh of the alpha shape is
saved/wrote in an external file. It can be simply the list of polygons and
their respective 3D vertices. I guess these polygons will be defining the
surface mesh of the alpha shape. If I can do that I can see the output of
the alpha shape generation program in an external tool I am familiar with.
I know this is very straightforward but I could not figure this out with my
limited knowledge of CGAL.
I know you gueys have the code but I am pasting it again for completion.
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Delaunay_triangulation_3.h>
#include <CGAL/Alpha_shape_3.h>
#include <fstream>
#include <list>
#include <cassert>
typedef CGAL::Exact_predicates_inexact_constructions_kernel Gt;
typedef CGAL::Alpha_shape_vertex_base_3<Gt> Vb;
typedef CGAL::Alpha_shape_cell_base_3<Gt> Fb;
typedef CGAL::Triangulation_data_structure_3<Vb,Fb> Tds;
typedef CGAL::Delaunay_triangulation_3<Gt,Tds> Triangulation_3;
typedef CGAL::Alpha_shape_3<Triangulation_3> Alpha_shape_3;
typedef Gt::Point_3 Point;
typedef Alpha_shape_3::Alpha_iterator Alpha_iterator;
int main()
{
std::list<Point> lp;
//read input
std::ifstream is("./data/bunny_1000");
int n;
is >> n;
std::cout << "Reading " << n << " points " << std::endl;
Point p;
for( ; n>0 ; n--) {
is >> p;
lp.push_back(p);
}
// compute alpha shape
Alpha_shape_3 as(lp.begin(),lp.end());
std::cout << "Alpha shape computed in REGULARIZED mode by default"
<< std::endl;
// find optimal alpha value
Alpha_iterator opt = as.find_optimal_alpha(1);
std::cout << "Optimal alpha value to get one connected component is "
<< *opt << std::endl;
as.set_alpha(*opt);
assert(as.number_of_solid_components() == 1);
return 0;
}
After searching a lot in the internet I found that probably we need to use something like
std::list<Facet> facets;
alpha_shape.get_alpha_shape_facets
(
std::back_inserter(facets),Alpha_shape::REGULAR
);
But I am still completely clueless how to use this in the above code!
As documented here, a facet is a pair (Cell_handle c,int i) defined as the facet in c opposite to the vertex of index i.
On this page, you have the description of how the vertex indices of a cell are.
In the following code sample, I added a small output that prints an OFF file on cout by duplicating the vertices. To do something clean, you can either use a std::map<Alpha_shape_3::Vertex_handle,int> to associate a unique index per vertex or add an info to the vertices like in those examples.
/// collect all regular facets
std::vector<Alpha_shape_3::Facet> facets;
as.get_alpha_shape_facets(std::back_inserter(facets), Alpha_shape_3::REGULAR);
std::stringstream pts;
std::stringstream ind;
std::size_t nbf=facets.size();
for (std::size_t i=0;i<nbf;++i)
{
//To have a consistent orientation of the facet, always consider an exterior cell
if ( as.classify( facets[i].first )!=Alpha_shape_3::EXTERIOR )
facets[i]=as.mirror_facet( facets[i] );
CGAL_assertion( as.classify( facets[i].first )==Alpha_shape_3::EXTERIOR );
int indices[3]={
(facets[i].second+1)%4,
(facets[i].second+2)%4,
(facets[i].second+3)%4,
};
/// according to the encoding of vertex indices, this is needed to get
/// a consistent orienation
if ( facets[i].second%2==0 ) std::swap(indices[0], indices[1]);
pts <<
facets[i].first->vertex(indices[0])->point() << "\n" <<
facets[i].first->vertex(indices[1])->point() << "\n" <<
facets[i].first->vertex(indices[2])->point() << "\n";
ind << "3 " << 3*i << " " << 3*i+1 << " " << 3*i+2 << "\n";
}
std::cout << "OFF "<< 3*nbf << " " << nbf << " 0\n";
std::cout << pts.str();
std::cout << ind.str();
Here is my code, which outputs vtk file for visualization in Paraview. Comparing with slorior's solutions, no duplicated points are saved in the file. But my code is just for the visualization, if you need to figure out the exterior or interior simplexes, you should modify the code to get these results.
void writevtk(Alpha_shape_3 &as, const std::string &asfile) {
// http://cgal-discuss.949826.n4.nabble.com/Help-with-filtration-and-filtration-with-alpha-values-td4659524.html#a4659549
std::cout << "Information of the Alpha_Complex:\n";
std::vector<Alpha_shape_3::Cell_handle> cells;
std::vector<Alpha_shape_3::Facet> facets;
std::vector<Alpha_shape_3::Edge> edges;
// tetrahedron = cell, they should be the interior, it is inside the 3D space
as.get_alpha_shape_cells(std::back_inserter(cells), Alpha_shape_3::INTERIOR);
// triangles
// for the visualiization, don't need regular because tetrahedron will show it
//as.get_alpha_shape_facets(std::back_inserter(facets), Alpha_shape_3::REGULAR);
as.get_alpha_shape_facets(std::back_inserter(facets), Alpha_shape_3::SINGULAR);
// edges
as.get_alpha_shape_edges(std::back_inserter(edges), Alpha_shape_3::SINGULAR);
std::cout << "The alpha-complex has : " << std::endl;
std::cout << cells.size() << " cells as tetrahedrons" << std::endl;
std::cout << facets.size() << " triangles" << std::endl;
std::cout << edges.size() << " edges" << std::endl;
size_t tetra_num, tri_num, edge_num;
tetra_num = cells.size();
tri_num = facets.size();
edge_num = edges.size();
// vertices: points <-> id
std::map<Point, size_t> points;
size_t index = 0;
// finite_.. is from DT class
for (auto v_it = as.finite_vertices_begin(); v_it != as.finite_vertices_end(); v_it++) {
points[v_it->point()] = index;
index++;
}
// write
std::ofstream of(asfile);
of << "# vtk DataFile Version 2.0\n\nASCII\nDATASET UNSTRUCTURED_GRID\n\n";
of << "POINTS " << index << " float\n";
for (auto v_it = as.finite_vertices_begin(); v_it != as.finite_vertices_end(); v_it++) {
of << v_it->point() << std::endl;
}
of << std::endl;
of << "CELLS " << tetra_num + tri_num + edge_num << " " << 5 * tetra_num + 4 * tri_num + 3 * edge_num << std::endl;
for (auto cell:cells) {
size_t v0 = points.find(cell->vertex(0)->point())->second;
size_t v1 = points.find(cell->vertex(1)->point())->second;
size_t v2 = points.find(cell->vertex(2)->point())->second;
size_t v3 = points.find(cell->vertex(3)->point())->second;
of << "4 " << v0 << " " << v1 << " " << v2 << " " << v3 << std::endl;
}
// https://doc.cgal.org/latest/TDS_3/classTriangulationDataStructure__3.html#ad6a20b45e66dfb690bfcdb8438e9fcae
for (auto tri_it = facets.begin(); tri_it != facets.end(); ++tri_it) {
of << "3 ";
auto tmp_tetra = tri_it->first;
for (int i = 0; i < 4; i++) {
if (i != tri_it->second) {
of << points.find(tmp_tetra->vertex(i)->point())->second << " ";
}
}
of << std::endl;
}
// https://doc.cgal.org/latest/TDS_3/classTriangulationDataStructure__3.html#af31db7673a6d7d28c0bb90a3115ac695
for (auto e : edges) {
of << "2 ";
auto tmp_tetra = e.get<0>();
int p1, p2;
p1 = e.get<1>();
p2 = e.get<2>();
of << points.find(tmp_tetra->vertex(p1)->point())->second << " "
<< points.find(tmp_tetra->vertex(p2)->point())->second << std::endl;
}
of << std::endl;
of << "CELL_TYPES " << tetra_num + tri_num + edge_num << std::endl;
for (int i = 0; i < tetra_num; i++) {
of << "10 ";
}
for (int i = 0; i < tri_num; i++) {
of << "5 ";
}
for (int i = 0; i < edge_num; i++) {
of << "3 ";
}
of << std::endl;
of.close();
}