CGAL users discussion list

[Andreas Fabri <>]

On 24/05/2010 20:12, Hansjoerg Seybold wrote:
> hello,
> I am trying to use the member function cdt.incident_constraints(va,done);

I am not sure what you mean with "done".

The signature of the function is

OutputIterator cdt.incicent_constraints(Vertex_handle va,
                                        OutputIterator out);



std::list<Edge> edges;

cdt.incident_constraints(std::back_inserter(edges));

Now you traverse the edge list the usual way.

If instead of storing the edges you could write your
own outout itertor class that does something on the
fly, whenever the next edge gets assigned to it.

Best regards,

andreas


> but i am not sure if i use the EdgeItOutput correctly.
>
> I first create a list with the iterators
> insert_iterator<list<Edge> > ei,done;
> and later iterate over the content of the list with list<Edge>::iterator
> eit;
> This looks a bit wired to me that i have to use a list where i store the
> edges first.
>
> Is there an example using these things in the CGAL demo/examples?
>
> Thanks a lot
>   hj
>
>
>
>
>
> On Sun, May 23, 2010 at 8:45 AM, Hansjoerg Seybold
> <
>  
> <mailto:>>
>  wrote:
>
>     Hi,
>     thanks a lot for the hints.
>     I had a deeper search in the reference manual and found the linewalk
>     function which could be used to walk along the constraint edges of
>     the PGLS.
>
>     The question is if the linewalk is save with respect to exact
>     predictions.
>     Otherwise i can also search along the constraint edges wwith
>     circulators until i reach the endpoint of the constraint PGLS edge.
>     thanks
>           hj
>
>
>
>
>
>     On Tue, May 18, 2010 at 5:32 PM, Mariette Yvinec
>     
> <
>     
> <mailto:>>
>  wrote:
>
>
>
>         Hansjoerg Seybold wrote:
> >         thanks for the answer, but i dont understand how i should mark
> >         the cells.
> >
> >
> >         assume i have an internal segment edge of the PLGS, which is
> >         devided into 3 parts by the insetion of 2 gabriel points.
> >         There are mesh cells
> >         left and right to the PLGS edge.
> >         How do i have to iterate the determine the cells which are
> >         left/right of the edge?
> >         or inide/outside of a polygon for example inside/outside of the
> >         triangular region in example 45.4
> >
> >         Can i mark the cells during the mesh generation to keep track
> >         on to which region they belong to?
> >
> >
> >         thanks a lot
> >            hj
>         You may mark the cells once the mesh is generated.
>         There is an example of such a marking in the file:
>         demo/Triangultion_2/Constrained_Delaunay_triangulation_2.cpp
>
>
>
> >         On Mon, May 17, 2010 at 2:38 PM, Mariette Yvinec
> >         
> > <
> >         
> > <mailto:>>
> >  wrote:
> >
> >             A better way, may be to mark the cells
> >             with some indexes of the subdomain they belong to.
> >             Using a propagation algorithm  through cell adjacency
> >             it is easy to mark the cells.
> >             Then knowing on which boundary
> >             are the edges is straightforward.
> >
> >             The main advantage is to avoid using
> >             geometric tests like is_colinear()
> >             which might yield a false result if you use floating point
> >             computations
> >             and is costly when using an EPIC Kernel.
> >
> >
> >             Hansjoerg Seybold wrote:
> > >             hello,
> > >             thanks a lot. This would help to determine weather
> > >             boundary or not.
> > >             For a fem mesh i further have to know on which boundary the
> > >             nodes are to apply the appropriate boundary conditions in
> > >             the calculations. Also for internal boundary conditions
> > >             the is_in_domain()
> > >             is not sufficient.
> > >             I was thinking to check all vvertices with all edges of
> > >             the PLGS with the basic functions
> > >             are_ordered_along line() or is_colinear() because i could
> > >             not find a better
> > >             point location method which returns the edge of the PLGS
> > >             for a given
> > >             vertex. Please let me know if you have a better
> > >             suggestion for me.
> > >
> > >             best hj
> > >
> > >
> > >
> > >
> > >
> > >             On Mon, May 17, 2010 at 10:51 AM, Mariette Yvinec
> > >             
> > > <
> > >             
> > > <mailto:>>
> > >  wrote:
> > >
> > >
> > >                 You may identify the boundary edges as edges incident
> > >                 to a single face that is in the doamain.
> > >                 This can be tested using the is_in_domain() member
> > >                 function
> > >                 of the  facet.
> > >
> > >                 Hansjoerg Seybold wrote:
> > > >                 Hello,
> > > >                 i could not find a function /flag in the mesher that
> > > >                 identifies the boundary
> > > >                 edges, meaning edges that are part of the initial PLGS.
> > > >                 I saw that for a 3D mesh a IS_BOUNDARY type exists.
> > > >                 but for 2d meshes i could not find an equivalence.
> > > >                 Do i have to check the boundary query by hand using
> > > >                 geometric queries for the vertex points of the mesh
> > > >                 and the  edges of the original PLGS?
> > > >
> > > >                 thanks a lot
> > > >                     hansjoerg
> > > >
> > > >
> > > >                 On Thu, Apr 22, 2010 at 3:31 PM, Hansjoerg Seybold
> > > >                 
> > > > <
> > > >                 
> > > > <mailto:>>
> > > >  wrote:
> > > >
> > > >                     Thanks for the reply.
> > > >
> > > >                      the mesh_domain thus is a simple triangulation
> > > >                     object.
> > > >
> > > >                     One question remains: how do i identify if the
> > > >                     newly inserted vertices (edge) is lying on the
> > > >                     original boundary
> > > >                     triangulation identify the boudnary of the mesh
> > > >                     domain
> > > >
> > > >                     thanks
> > > >
> > > >
> > > >                     On Thu, Apr 22, 2010 at 2:01 PM, Ramin H
> > > >                     
> > > > <
> > > >  
> > > > <mailto:>>
> > > >                     wrote:
> > > >
> > > >                         Look here:
> > > >                         
> > > > http://www.cgal.org/Manual/last/doc_html/cgal_manual/Triangulation_2_ref/Class_Triangulation_2.html
> > > >
> > > >                         /typedef Tds::Face_iterator /
> > > >                         /All_faces_iterator; /  iterator over all
> > > >                         faces.
> > > >                         / typedef Tds::Edge_iterator /
> > > >                         /All_edges_iterator; /  iterator over all edges
> > > >                         / typedef Tds::Vertex_iterator /
> > > >                         /All_vertices_iterator; /       iterator over all
> > > >                         vertices
> > > >
> > > >
> > > >
> > > >                         -Ramin
> > > >
> > > >
> > > >                         On Thu, Apr 22, 2010 at 5:44 AM, Hansjoerg
> > > >                         Seybold 
> > > > <
> > > >                         
> > > > <mailto:>>
> > > >  wrote:
> > > >
> > > >                             hello,
> > > >                             I am trying to make a simple 2D mesher
> > > >                             for a FEM code using the cgal meshing
> > > >                             capabilities.
> > > >
> > > >                              I experimenteeeed with the meshing
> > > >                             examples and demos. What i could not
> > > >                             find in the
> > > >                             documentation and the examples is
> > > >
> > > >                             How can i iterate through the mesh,
> > > >                             Faces, Vertices, Edges?
> > > >
> > > >                             Is there a method to determine if a
> > > >                             edge/vertex lies on a boundary (meaning
> > > >                             part of the CDT which is used as input
> > > >                             for the mesher?
> > > >
> > > >                             Are there default io streams for the meshs?
> > > >
> > > >                             It would be nice if anybody has some
> > > >                             suggestions references for
> > > >                             documentation etc on this topic.
> > > >
> > > >                             Thanks a lot
> > > >                                best hansjoerg
> > >
> > >                 --
> > >                 Mariette Yvinec
> > >                 Geometrica project team
> > >                 INRIA  Sophia-Antipolis
> >
> >             --
> >             Mariette Yvinec
> >             Geometrica project team
> >             INRIA  Sophia-Antipolis
>
>         --
>         Mariette Yvinec
>         Geometrica project team
>         INRIA  Sophia-Antipolis