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[urhere <>]

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
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