CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

The edge type is documented here:

http://www.cgal.org/Manual/latest/doc_html/cgal_manual/TriangulationDS_3_ref/Concept_TriangulationDataStructure_3.html#Cross_link_anchor_1333

typedef Triple<Cell_handle, int, int> Edge;

This is a triple that contains a pointer to a cell and the two indices
of the vertices corresponding to the edge.

S.


urhere wrote:
> I have just started using CGAL for a project that works with tessellations
> from NURBS surfaces (using OpenGL). I have been able to write out the
> vertices from a tessellation, triangulate them with
> Delaunay_triangulation_2, compute and store normals for the faces, and do
> some basic face and vertex iteration. All has gone well and I'm pretty
> thrilled with the results so far. Right now I need to:
>
>   --look at all edges in the triangulation and
>   --compare the visibility of the adjacent faces (determined by the
> orientation of the normals 
>      relative to a viewpoint). 
>
> Although the method in the code below does what I need, it's probably
> visiting edges more than once. It seems like I ought to be able to do this
> pretty simply with an Edge_iterator but I have been baffled by the indexing
> needed to look up the faces bordering an edge (I can find the endpoints ok).
> I would greatly appreciate any snippets of code or pointers to appropriate
> places in the manuals for information on navigating with Edge_iterators.
>
> Here's the code (everything is written out explicitly so I could figure out
> the indexing):
>
>
> 	for (Delaunay::Vertex_iterator vit=dt.finite_vertices_begin(); 
>                    vit != dt.finite_vertices_end(); ++vit) {
>                 // Get the face associated with the current vertex
>                 Face_handle currentFh = vit->face();
>                 // Get the counter clockwise neighbor of this face
> 		Face_handle ccwFh = 
>                             
> vit->face()->neighbor(currentFh->ccw(currentFh->index ( vit) ));
>                 // Get the clockwise neighbor of this face
> 		Face_handle cwFh = 
>                             
> vit->face()->neighbor(currentFh->cw(currentFh->index ( vit) ));
>                 // Get the normals for both faces (previously stored)
>                 Vector_3 faceNormalNormalizedCurrent = currentFh->info();
> 		Vector_3 faceNormalNormalizedCCW = ccwFh->info(); 
> 		Vector_3 faceNormalNormalizedCW = cwFh->info(); 
> 		// Get the vertex indices and handles
>                 int currentVertexIndex = currentFh->index ( vit);
> 		int ccwVertexIndex = currentFh->ccw(currentFh->index ( vit)); 
> 		int cwVertexIndex = currentFh->cw(currentFh->index ( vit)); 
> 		Vertex_handle ccwVh = currentFh->vertex(ccwVertexIndex);
>                 Vertex_handle cwVh = currentFh->vertex(cwVertexIndex);
>                            // Get the coordinates
>                 Point_3 currentPoint = vit->point();
>                 Point_3 ccwPoint = ccwVh->point();
>                 Point_3 cwPoint = cwVh->point();
>                            // The rest of the code is irrelevant but I use
> currentPoint, ccwPoint, and
>                            // cwPoint to draw edges, if necessary
>               }
>  
> Thanks for any insights.
> Jim