# Geometry :

Subject: [ggl] Help needed with Intersection operation
From: angusj (awj1958)
Date: 2011-08-13 19:52:25

The following intersection operation returns the second hole in the green
polygon.

Since I've only just started playing with boost geometry, I presume I'm
doing something wrong.

typedef boost::geometry::model::polygon ggl_polygon;
typedef boost::geometry::model::multi_polygon ggl_polygons;

ggl_polygon blue, green;
"POLYGON((2 1.3,2.4 1.7,2.8 1.8,3.4 1.2,3.7 1.6,3.4 2,4.1 3,5.3
2.6,5.4 1.2,4.9 0.8,2.9 0.7,2 1.3)"
"(4.0 2.0, 4.2 1.4, 4.8 1.9, 4.4 2.2, 4.0 2.0)(2.8 1.1,3.3
1.1,2.8 1.6))", green);
"POLYGON((4.0 -0.5 , 3.5 1.0 , 2.0 1.5 , 3.5 2.0 , 4.0 3.5 , 4.5 2.0
, 6.0 1.5 , 4.5 1.0 , 4.0 -0.5))", blue);

ggl_polygons output;
boost::geometry::intersection(green, blue, output);

for (ggl_polygons::iterator it = output.begin(); it != output.end(); ++it)
{
for (ggl_polygon::ring_type::size_type j = 0; j < it->outer().size(); ++j)
cout << it->outer()[j].x() << ", " << it->outer()[j].y() << "\n";
cout << "\n";

for (ggl_polygon::inner_container_type::size_type i = 0; i <
it->inners().size(); ++i)
{
for (ggl_polygon::ring_type::size_type j = 0; j < it->inners()[i].size();
++j)
cout << it->inners()[i][j].x() << ", " << it->inners()[i][j].y() <<
"\n";
cout << "\n";
}
}

Thanks for any help ...

Angus

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