CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Here is what I meant by "with simplex types suited for the Alpha-shape"

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Alpha_shape_vertex_base_2<K> Vbb;
typedef CGAL::Alpha_shape_face_base_2<K>  Fb;
typedef CGAL::Triangulation_vertex_base_with_info_2<std::size_t, K, Vbb> Vb;
typedef CGAL::Triangulation_data_structure_2<Vb,Fb> Tds;
typedef CGAL::Delaunay_triangulation_2<K,Tds> Triangulation_2;
typedef CGAL::Alpha_shape_2<Triangulation_2>  Alpha_shape_2;

Sebastien.

On 05/30/2014 07:44 PM, morrischen2008 wrote:
> Thanks a lot Sebastien. Your advice works.
>
> Following your advice [1], I successfully created the Delaunay
> triangulation with "index inserted in the vertices".
>
> However, I failed to use the established Delaunay triangulation to build
> the alpha shape [3].
>
> Here is how I did it.
>
> typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
> typedef K::FT FT;
> typedef CGAL::Triangulation_vertex_base_with_info_2<unsigned, K> Vb;
> typedef CGAL::Triangulation_data_structure_2<Vb,> Tds;
> typedef CGAL::Delaunay_triangulation_2<K, Tds> Delaunay_2;
> typedef CGAL::Alpha_shape_2<Delaunay>  Alpha_shape_2;
>
> Delaunay_2 T;
> T.insert(points.begin(), points.end()); // Compile and runs fine until now
> Alpha_shape_2 A(T); // compiler gives lots of errors!!!
>
>
> Previously when I just used a bunch of points to construct alpha shape
> it works fine, like this:
>
>
> typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
> typedef K::FT FT;
> typedef CGAL::Alpha_shape_vertex_base_2<K> Vb;
> typedef CGAL::Alpha_shape_face_base_2<K>  Fb;
> typedef CGAL::Triangulation_data_structure_2<Vb,Fb> Tds;
> typedef CGAL::Delaunay_triangulation_2<K,Tds> Triangulation_2;
> typedef CGAL::Alpha_shape_2<Triangulation_2>  Alpha_shape_2;
>
> Alpha_shape_2 A(input.begin(), input.end()); // Works fine
>
> Any advice to get rid of the compiler errror? I will highly appreciate
> it. Thanks.
>
>
>
>
>
> On Thu, May 29, 2014 at 1:09 AM, Sebastien Loriot (GeometryFactory) [via
> cgal-discuss] <[hidden email]
> </user/SendEmail.jtp?type=node&node=4659367&i=0>> wrote:
>
>     You can try to build the triangulation (with simplex types suited for
>     the Alpha-shape of course) like in this example [1] or any
>     "insert_with_info*" example [2].
>     Then you can build the alpha shape from the triangulation [3].
>
>     Sebastien.
>
>     [1]
>     
> http://doc.cgal.org/latest/Triangulation_2/Triangulation_2_2info_insert_with_pair_iterator_2_8cpp-example.html
>     [2] http://doc.cgal.org/latest/Triangulation_2/examples.html
>     [3]
>     
> http://doc.cgal.org/latest/Alpha_shapes_2/classCGAL_1_1Alpha__shape__2.html#a9d026da2568aed80884a5053bae0039b
>     On 05/28/2014 09:24 PM, morrischen2008 wrote:
>
>      > Hi everyone,
>      >
>      > I am currently using Alpha Shape to construct the surface of a
>     bunch of
>      > points. The process is simple: the input is a bunch of points,
>     and I get a
>      > bunch of points as output. However, when I have indexes for the
>     input
>      > points, like this
>      >
>      > input
>      > ---------------
>      > index  location
>      > 1       (1.0, 2.0)
>      > 2       (2.1, 2.3)
>      > 3       (2.3, 1.8)
>      > .             ...
>      > .             ...
>      > 731   (7.1, 9.3)
>      > .             ...
>      >
>      > I want to have to get, in the output points, also the indexes,
>     like this
>      >
>      > output
>      > ------------------
>      > index    location
>      > 2          (2.1, 2.3)
>      > .                 ...
>      > .                 ...
>      > 333      (3.5, 7.8)
>      > .                ...
>      >
>      > However, I do not know how to obtain the indexes in outputs.
>     Anyone here can
>      > help me with this? I will appreciate your kind help. Below is how
>     I obtain
>      > the output points.
>      >
>      > First, use the constructor
>      >
>      > Alpha_shape_2 A(input.begin(), input.end(), FT(0.0001));
>      >
>      > , while "input" is  a "list<Point_2>".
>      >
>      > The output I can obtain from "A" is a bunch of points, by using the
>      > iterators (I know I can also get a bunch of "Segment_2 as outputs
>     as well"),
>      > like this
>      >
>      > for(Alpha_shape_vertices_iterator it =
>       A.alpha_shape_vertices_begin();
>      >        it != A.alpha_shape_vertices_end();
>      >        ++it) {
>      >      Vertex_handle vh = *it;
>      >      Point_2 p(vh->point().x(), vh->point().y());
>      >      output.push_back(p);
>      > }
>      >
>      > , while "output" is a "vector<Point_2>".
>      >
>      >
>      >
>      > --
>      > View this message in context:
>     
> http://cgal-discuss.949826.n4.nabble.com/Alpha-Shape-2D-Input-point-index-tp4659360.html
>      > Sent from the cgal-discuss mailing list archive at Nabble.com.
>      >
>
>
>     --
>     You are currently subscribed to cgal-discuss.
>     To unsubscribe or access the archives, go to
>     https://sympa.inria.fr/sympa/info/cgal-discuss
>
>
>
>
>     ------------------------------------------------------------------------
>     If you reply to this email, your message will be added to the
>     discussion below:
>     
> http://cgal-discuss.949826.n4.nabble.com/Alpha-Shape-2D-Input-point-index-tp4659360p4659362.html
>
>     To unsubscribe from Alpha Shape 2D: Input point index, click here.
>     NAML
>     
> <http://cgal-discuss.949826.n4.nabble.com/template/NamlServlet.jtp?macro=macro_viewer&id=instant_html%21nabble%3Aemail.naml&base=nabble.naml.namespaces.BasicNamespace-nabble.view.web.template.NabbleNamespace-nabble.view.web.template.NodeNamespace&breadcrumbs=notify_subscribers%21nabble%3Aemail.naml-instant_emails%21nabble%3Aemail.naml-send_instant_email%21nabble%3Aemail.naml>
>
>
>
>
>
> --
> Morris
>
> ------------------------------------------------------------------------
> View this message in context: Re: Alpha Shape 2D: Input point index
> <http://cgal-discuss.949826.n4.nabble.com/Alpha-Shape-2D-Input-point-index-tp4659360p4659367.html>
> Sent from the cgal-discuss mailing list archive
> <http://cgal-discuss.949826.n4.nabble.com/> at Nabble.com.