CGAL users discussion list

[Bob Bill <>]

Thanks a lot Andreas for your quick reply! Even if I add:

cdt.insert_constraint(va,vb);

for all the couples as done in this example (https://doc.cgal.org/latest/Mesh_2/Mesh_2_2conforming_8cpp-example.html#a3) I still get as result 0. I don't see what I'm doing wrong.

Best,

Bob

Il venerdì 17 febbraio 2023, 11:07:07 CET, Andreas Fabri <> ha scritto:

You only insert points.

For a domain you have to insert polygons or segments that spit up the plane.

On 2/17/2023 10:59 AM, Bob Bill ( via cgal-discuss Mailing List) wrote:

Hi,

I need to determine if a Point is inside or outside a 2D mesh (in particular a constrained Delaunay triangulation). I’ve found the answer to this question (https://stackoverflow.com/questions/22448060/how-to-determine-a-point-is-inside-2d-mesh-or-not-cgal) on SO, but I can’t understand why this query is always negative in my particular application. Please see the following MWE, where the origin is not recognised as an internal point.

I don't see what is the problem, any hint is highly appreciated.

Best,

Bob

#include <CGAL/Constrained_Delaunay_triangulation_2.h>

#include <CGAL/Delaunay_mesh_face_base_2.h>

#include <CGAL/Delaunay_mesh_size_criteria_2.h>

#include <CGAL/Delaunay_mesher_2.h>

#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>

#include <CGAL/Triangulation_conformer_2.h>

#include <iostream>

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;

typedef CGAL::Triangulation_vertex_base_2<K> Vb;

typedef CGAL::Delaunay_mesh_face_base_2<K> Fb;

typedef CGAL::Triangulation_data_structure_2<Vb, Fb> Tds;

typedef CGAL::Constrained_Delaunay_triangulation_2<K, Tds> CDT;

typedef CDT::Point Point_2;

typedef CDT::Vertex_handle Vertex_handle;

int main() {

CDT cdt;

// construct a constrained triangulation

Vertex_handle va = cdt.insert(Point_2(5., 5.));

Vertex_handle vb = cdt.insert(Point_2(-5., 5.));

Vertex_handle vc = cdt.insert(Point_2(4., 3.));

Vertex_handle vd = cdt.insert(Point_2(5., -5.));

Vertex_handle ve = cdt.insert(Point_2(6., 6.));

Vertex_handle vf = cdt.insert(Point_2(-6., 6.));

Vertex_handle vg = cdt.insert(Point_2(-6., -6.));

Vertex_handle vh = cdt.insert(Point_2(6., -6.));

std::cout << "Number of vertices before: " << cdt.number_of_vertices()

<< std::endl;

typename CDT::Face_handle fh = cdt.locate(Point_2{0., 0.});

std::cout << fh->is_in_domain() << std::endl;

}

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-- 
Andreas Fabri, PhD
Chief Officer, GeometryFactory
Editor, The CGAL Project

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