// Boost.Geometry (aka GGL, Generic Geometry Library) // QuickBook Example // Copyright (c) 2011-2012 Barend Gehrels, Amsterdam, the Netherlands. // Use, modification and distribution is subject to the Boost Software License, // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at // http://www.boost.org/LICENSE_1_0.txt) //[correct //` Shows how to correct a polygon with respect to its orientation and closure #include <iostream> #include <boost/geometry.hpp> #include <boost/geometry/geometries/polygon.hpp> #include <boost/geometry/geometries/adapted/boost_tuple.hpp> BOOST_GEOMETRY_REGISTER_BOOST_TUPLE_CS(cs::cartesian) #include <boost/assign.hpp> int main() { using boost::assign::tuple_list_of; typedef boost::geometry::model::polygon < boost::tuple<int, int> > clockwise_closed_polygon; clockwise_closed_polygon cwcp; // Fill it counterclockwise (so wrongly), forgetting the closing point boost::geometry::exterior_ring(cwcp) = tuple_list_of(0, 0)(10, 10)(0, 9); // Add a counterclockwise closed inner ring (this is correct) boost::geometry::interior_rings(cwcp).push_back(tuple_list_of(1, 2)(4, 6)(2, 8)(1, 2)); // Its area should be negative (because of wrong orientation) // and wrong (because of omitted closing point) double area_before = boost::geometry::area(cwcp); // Correct it! boost::geometry::correct(cwcp); // Check its new area double area_after = boost::geometry::area(cwcp); // And output it std::cout << boost::geometry::dsv(cwcp) << std::endl; std::cout << area_before << " -> " << area_after << std::endl; return 0; } //] //[correct_output /*` Output: [pre (((0, 0), (0, 9), (10, 10), (0, 0)), ((1, 2), (4, 6), (2, 8), (1, 2))) -7 -> 38 ] */ //]