CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

With the 3.8-beta1 release of CGAL:

http://www.cgal.org/Manual/beta/doc_html/cgal_manual/Triangulation_2/Chapter_main.html#Subsection_35.11.2

For the projection, you may be interested by this example:
http://www.cgal.org/Manual/beta/doc_html/cgal_manual/Triangulation_2/Chapter_main.html#Subsection_35.5.2

S.

Adrian B wrote:
> How can I associate indices to
> CGAL::Exact_predicates_inexact_constructions_kernel::Point_2 points in
> the same order as the points are inserted into a Delaunay
> triangulation structure?
>
> Background:
> In my current project I create a number of 3D points, each of which
> has a colour, to represent a terrain. Each point is therefore
> described by its x-, y-, z-, r-, g- and b-value. Now I want to mesh
> them for creating a surface model, which I safe as a ply-file. To do
> so, I project the points into the x-y plane and apply 2D Delaunay
> triangulation for generating the connections. The z-coordinate, as
> well as the RGB values are preserved. In the end I need to output the
> points (x, y, z, r, g, b) toghether with the triplets of point's
> indicies, which define the triangles.
> On 
> http://www.cgal.org/Manual/3.8-beta1/doc_html/cgal_manual/BGL/Chapter_main.html
> section 72.5.2 I found a way of associating an index to a vertex.
> The problem is now, that the indices are apparantly not associated in
> the same order as the points (vertices) were added. Therefore the
> vertex IDs point to complete different input points than the line
> number in my input file. This is my code so far:
>
> #include <fstream>
> #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
> #include <CGAL/Delaunay_triangulation_2.h>
> #include <CGAL/Triangulation_vertex_base_with_id_2.h>
> #include <CGAL/boost/graph/graph_traits_Delaunay_triangulation_2.h>
>
> #include <climits>
> #include <boost/graph/dijkstra_shortest_paths.hpp>
> #include <boost/graph/filtered_graph.hpp>
>
> typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
> typedef K::Point_2 Point;
>
> typedef CGAL::Triangulation_vertex_base_with_id_2<K> Tvb;
> typedef CGAL::Triangulation_face_base_2<K> Tfb;
> typedef CGAL::Triangulation_data_structure_2<Tvb,Tfb> Tds;
> typedef CGAL::Delaunay_triangulation_2<K, Tds> Triangulation;
>
> template <typename T>
> struct Is_finite {
>
>   const T* t_;
>
>   Is_finite()
>     : t_(NULL)
>   {}
>
>   Is_finite(const T& t)
>     : t_(&t)
>   { }
>
>   template <typename VertexOrEdge>
>   bool operator()(const VertexOrEdge& voe) const {
>     return ! t_->is_infinite(voe);
>   }
> };
>
> typedef Is_finite<Triangulation> Filter;
> typedef boost::filtered_graph<Triangulation,Filter,Filter> 
> Finite_triangulation;
> typedef boost::graph_traits<Finite_triangulation>::vertex_descriptor
> vertex_descriptor;
> typedef boost::graph_traits<Finite_triangulation>::vertex_iterator
> vertex_iterator;
>
> int main()
> {
>         Triangulation dt;
>         Filter is_finite(dt);
>         Finite_triangulation ft(dt, is_finite, is_finite);
>         vertex_iterator vit, ve;
>         int index = 0, nbVertices = 0;
>         const int  maxLineLength = 200;
>         char line[maxLineLength];
>         float x,y,z;
>         int r,g,b;
>         std::ifstream fPoints("D:/input_file.txt");
>         std::ofstream fPointsAndMeshOut;
>         std::ifstream fPointsAndMeshIn;
>         std::string path_pointsAndMeshFile= "D:/temp_file.txt";
>         std::ofstream fPly("D:/output_file.ply");
>
>         fPointsAndMeshOut.open(path_pointsAndMeshFile.c_str());
>         fPointsAndMeshOut << std::setprecision(4);
>         while (!fPoints.eof()) {
>                 fPoints.getline(line, maxLineLength);
>                 sscanf(line, "%f, %f, %f, %d, %d, %d", &x, &y, &z, &r, &g, 
> &b);
>                 fPointsAndMeshOut << std::fixed << x << " " << y << " " << z << " 
> "
> << r << " " << g << " " << b << std::endl;
>                 dt.insert(Point(x,y));
>                 nbVertices++;
>         }
>         fPoints.close();
>
>         for(boost::tie(vit,ve)=boost::vertices(ft); vit!=ve; ++vit ){
>                 vertex_descriptor  vd = *vit;
>                 vd->id()= index++;
>                 vd->point();
>         }
>         
>         Triangulation::Finite_faces_iterator it;
>         for (it = dt.finite_faces_begin(); it != dt.finite_faces_end(); it++)
>         {
>                 fPointsAndMeshOut << "3 "  << it->vertex(0)->id() << " "  <<
> it->vertex(1)->id() << " "  << it->vertex(2)->id() << std::endl;  //
> Here the IDs don't correspond to the line number in the input file,
> producing a meaningless file here
>         }
>         fPointsAndMeshOut.close();
>
>         fPly << "ply" << std::endl;
>         fPly << "format ascii 1.0" << std::endl;
>         fPly << "element vertex " << nbVertices << std::endl;
>         fPly << "property float x" << std::endl;
>         fPly << "property float y" << std::endl;
>         fPly << "property float z" << std::endl;
>         fPly << "property uchar red" << std::endl;
>         fPly << "property uchar green" << std::endl;
>         fPly << "property uchar blue" << std::endl;
>         fPly << "element face " << dt.number_of_faces() << std::endl;
>         fPly << "property list uchar int vertex_index" << std::endl;
>         fPly << "end_header" << std::endl;
>
>         fPointsAndMeshIn.open(path_pointsAndMeshFile.c_str());
>         while (!fPointsAndMeshIn.eof()) {
>                 fPointsAndMeshIn.getline(line, maxLineLength);
>                 fPly << line << std::endl;
>         }
>         fPointsAndMeshIn.close();
>         fPly.close();
>
>         return 0;
> }
>
>
> Needless to say that the mesh output like this is compeltely wrong,
> with triangles going all over the place but for sure nothing like in a
> smooth mesh model.
> Therefore my question: How can I associate the indices (IDs) in the
> same order as the points are added?