...one of the most highly
regarded and expertly designed C++ library projects in the
world.

— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards

Corrects a geometry: all rings which are wrongly oriented with respect to their expected orientation are reversed. To all rings which do not have a closing point and are typed as they should have one, the first point is appended. Also boxes can be corrected.

template<typename Geometry> void correct(Geometry & geometry)

Type |
Concept |
Name |
Description |
---|---|---|---|

Geometry & |
Any type fulfilling a Geometry Concept |
geometry |
A model of the specified concept which will be corrected if necessary |

Either

`#include <boost/geometry/geometry.hpp>`

Or

`#include <boost/geometry/algorithms/correct.hpp>`

Case |
Behavior |
---|---|

Ring |
Ring is corrected |

Polygon |
Polygon is corrected |

Multi Polygon |
Multi Polygon is corrected |

Rectangle |
Rectangle is corrected with respect to minimal and maximal corners |

Other geometries |
Nothing happens, geometry is unchanged |

Tip | |
---|---|

Correct is not defined within OGC or ISO |

Linear

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; }

Output:

(((0, 0), (0, 9), (10, 10), (0, 0)), ((1, 2), (4, 6), (2, 8), (1, 2))) -7 -> 38