CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 05/04/2013 02:10 PM, Michael Kalygin wrote:
> Hello everyone! I was trying to find a solution on the forum. But it
> seems that the problem is quite specific. Let me describe it. First of
> all I'm using the next data structures:
>
> typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
> typedef CGAL::Triangulation_vertex_base_with_info_3<double, K>  Vb;
> typedef CGAL::Triangulation_data_structure_3  Tds;
> typedef CGAL::Delaunay_triangulation_3<K, Tds>  Delaunay;
> typedef K::Segment_3 Segment;
> typedef K::Point_3 Point;
>
> Note, that I'm using vertices with info, I need info() field to store my
> custom data about vertices.
>
> *The Method:* I have a method in my class, which finds a triangle of
> Delaunay triangulation intersecting with segment [p, 0), where p and 0
> are vectors in 3D space (p is an input parameter). The intersection
> exists with guarantee and this intersection is a point. When the method
> finds an intersection, it returns founded triangle. As a side effect it
> assigns point of intersection to p.
>
> *The Problem:* When I get triangle in the method, I actually lose info()
> in its vertices. I need to get this info without any additional
> operations. Previously, I was using nearest_vertex() method of a
> triangulation, but it looks like a needless operation which slows down
> my algorithm.
>
> tr.vertex(0).info();*// This field doesn't exist.*
>
> *The question:* Is there a way to get a triangle with info() in its
> vertices?
No, but you can still store the information outside of the class of use
a Facet together with the triangle (or simply use a Facet and create the
triangle on-the-fly is you only need it once).


> *Additional question:* Is there a simple way to mark a cell, from which
> I need to start a search of such triangle?
You can locate a cell containing p (using "locate" function) and walk 
from cells to cells.

Sebastien.

> *The Code:*
>
> Delaunay::Triangle ADMath::ProjectAndLocatePoint(Point&p)
> {
>      const double EPS = 0.01;
>      Delaunay::Triangle tr;
>      Segment seg = Segment(p, Point(p.x() * EPS, p.y() * EPS, p.z() * EPS)); 
> // Segment with excluded (0, 0, 0).
>      CGAL::Object intersection;
>
>      for (Delaunay::Finite_facets_iterator fit = 
> ADMath::triangulation->finite_facets_begin(); fit != 
> ADMath::triangulation->finite_facets_end(); ++fit) {
>          tr = ADMath::triangulation->triangle(*fit);*// THE PROBLEM IS HERE*
>
>          if (CGAL::do_intersect(seg, tr)) {
>              intersection = CGAL::intersection(seg, tr);
>              p = *CGAL::object_cast(&intersection); // Set p to its 
> projection on the triangle.
>              break;
>          }
>      }
>
>      return tr;
> }
>
>
> ------------------------------------------------------------------------
> View this message in context: Delaunay 3D: Get triangle with info in
> vertices.
> <http://cgal-discuss.949826.n4.nabble.com/Delaunay-3D-Get-triangle-with-info-in-vertices-tp4657355.html>
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