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[Alejandro Aguilar Sierra <>]

Hello:

I modified the greene_approx_convex_partition_2.cpp example to work
with a shape file I have. The only significant change is that instead
of giving a list of integer pairs in the function make_polygon I feed
the polygon with the result of a polygon from the shapefile. They are
all floats. It compiles perfectly and runs fine with the original
polygon, but when I my polygon, I got this error:


terminate called after throwing an instance of 'CGAL::Precondition_exception'
  what():  CGAL ERROR: precondition violation!
Expr: is_simple_2(first, last, traits)
File: /usr/include/CGAL/Polygon_2/Polygon_2_algorithms_impl.h
Line: 420
Aborted

The piece of code I modified is this, a Vectorvertex is a C++ generic
vector of this struct:

typedef struct {
  double x, y;
} vertex;

void make_polygon2(Polygon_2& polygon, Vectorvertex plate)
{
  for (unsigned int i=0; i < plate.size(); i++) {
    Point_2 p = Point_2(plate[i].x, plate[i].y);
    polygon.push_back(p);
    cout << p << endl;
  }
}

In the original main part of the example I just add a couple of lines
to loads the shapes and create a polygon from one of them:


int main(int argc, char** argv)
{
  Polygon_2    polygon;
  Polygon_list partition_polys;
  Traits       partition_traits;

  // Load the tectonic plates shapefile
  plates.load_shapes("today");
  Vectorvertex plate = plates.getPlate(201);
  make_polygon2(polygon, plate);

  CGAL::greene_approx_convex_partition_2(polygon.vertices_begin(),
                                         polygon.vertices_end(),
                                         std::back_inserter(partition_polys),
                                         partition_traits);

  assert(CGAL::convex_partition_is_valid_2(polygon.vertices_begin(),
                                           polygon.vertices_end(),
                                           partition_polys.begin(),
                                           partition_polys.end(),
                                           partition_traits));
  return 0;
}

The header is the same as in the example.

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Partition_traits_2<K>                         Traits;
typedef Traits::Point_2                                     Point_2;
typedef Traits::Polygon_2                                   Polygon_2;
typedef Polygon_2::Vertex_iterator                          Vertex_iterator;
typedef std::list<Polygon_2>                                Polygon_list;
typedef CGAL::Creator_uniform_2<int, Point_2>               Creator;
typedef CGAL::Random_points_in_square_2< Point_2, Creator > Point_generator;

I will appreciate any hint.

Au revoir.

-- A.