CGAL users discussion list

[Chris Marsh <>]

Oh, no auto is too bad. In this case, it's triangulation::Vertex_handle and triangulation::Face_handle. You have to use the template derived class.

I've updated the SO to make this more clear. Does this let you compile now?

So far, I am using purely 2D points (no “z” coordinate) for a 2D
triangulation. I may be using 3D meshes later, but not now.

Ok, with my example just set z to be 0 then. You can use a different geometry trait instead, but I'll be honest, I don't know which one that is. At the moment having a z=0 won't impact you at all.

I fear it won't really help you, but on off chance it does, this is a section of code where I build the CGAL data structure from a file

https://github.com/Chrismarsh/CHM/blob/master/src/mesh/triangulation.cpp#L232

The file that is being read in has 3 components: a vertex list, a face (elem) list, and a neighbour list.

The vertex list is a tuple holding the x,y,z coordinates (this is an earth surface model).

The face list is a tuple where each item is an index into the vertex list -- so [567,1,299] would mean that this i-th face is made up of the 567-th, 1-th, and 299-th vertexes

The neigh list is a tuple but is an index into the face list, for which faces are neighbours.

e.g.,

vertexes = [ 
  [x1,y1,z1],
  [x2,y2,z2],
  [x3,y3,z3]
]

# a single triangle made up of vertexes 0,1, and 2
triangles = [
  [0,1,2]
]

This is a pretty common format, and I suspect the gmsh format uses something like this.

Now, as there are thousands of vertices and thousands of faces in the
meshes I am using, I cannot create a new variable for each.

The general approach with millions of faces is to, while reading in the gmsh/whatever file, you create the 3 vertexes, insert the face, and move on.

Cheers

Chris

Chris Marsh
PhD Candidate
chrismarsh.ca

On Thu, 8 Nov 2018 at 18:06, Yoann LE BARS <> wrote:

Hello everybody out there!

On 2018/11/08 at 11:31 pm, Chris Marsh wrote:
> I've updated the SO post with a full working example w/ all header
> includes & a cmake script to build it. It adds 3 vertices and inserts 1
> face.

        Far more than I could have expected, thank you. I have used it to check
my own CMake script, it turned out there was several mistakes.

        Now, as there are thousands of vertices and thousands of faces in the
meshes I am using, I cannot create a new variable for each. I need to
stock them in vectors, and cannot use “auto”. Therefore, I am looking
for the appropriate type. It turned out
“CGAL::Triangulation_data_structure_2::Vertex_handle” is not
appropriate, as it does not provide “set_point”:

/home/yoann/program/UWWatch-test/src/gmsh.cpp:131:27: error:
‘__gnu_cxx::__alloc_traits<std::allocator<CGAL::internal::CC_iterator<CGAL::Compact_container<CGAL::Triangulation_vertex_base_2<CGAL::Projection_traits_xy_3<CGAL::Epick>,
CGAL::Triangulation_ds_vertex_base_2<CGAL::Triangulation_data_structure_2<CGAL::Triangulation_vertex_base_2<CGAL::Projection_traits_xy_3<CGAL::Epick>
>,
CGAL::Constrained_triangulation_face_base_2<CGAL::Projection_traits_xy_3<CGAL::Epick>
> > > >, CGAL::Default, CGAL::Default, CGAL::Default>, false> >,
CGAL::internal::CC_iterator<CGAL::Compact_container<CGAL::Triangulation_vertex_base_2<CGAL::Projection_traits_xy_3<CGAL::Epick>,
CGAL::Triangulation_ds_vertex_base_2<CGAL::Triangulation_data_structure_2<CGAL::Triangulation_vertex_base_2<CGAL::Projection_traits_xy_3<CGAL::Epick>
>,
CGAL::Constrained_triangulation_face_base_2<CGAL::Projection_traits_xy_3<CGAL::Epick>
> > > >, CGAL::Default, CGAL::Default, CGAL::Default>, false>
>::value_type’ {aka ‘class
CGAL::internal::CC_iterator<CGAL::Compact_container<CGAL::Triangulation_vertex_base_2<CGAL::Projection_traits_xy_3<CGAL::Epick>,
CGAL::Triangulation_ds_vertex_base_2<CGAL::Triangulation_data_structure_2<CGAL::Triangulation_vertex_base_2<CGAL::Projection_traits_xy_3<CGAL::Epick>
>,
CGAL::Constrained_triangulation_face_base_2<CGAL::Projection_traits_xy_3<CGAL::Epick>
> > > >, CGAL::Default, CGAL::Default, CGAL::Default>, false>’} has no
member named ‘set_point’

> Because I am using this for terrain, I use x,y,z points and use the
> projection trait to allow for using this 3D point in a 2D triangulation.
> I've kept it this way as it may be of use to you.

        So far, I am using purely 2D points (no “z” coordinate) for a 2D
triangulation. I may be using 3D meshes later, but not now.

> I hope this helps,
        Well, I have spent a couple of days trying to sort this out by myself
and failed. Now, I am making some progress, so it clearly helps.

        Best regards.

--
Yoann LE BARS
http://le-bars.net/yoann/
Diaspora* :

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