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

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

Clears a linestring, ring or polygon (exterior+interiors) or multi*.

Generic function to clear a geometry. All points will be removed from the collection or collections making up the geometry. In most cases this is equivalent to the .clear() method of a std::vector<...>. In the case of a polygon, this clear functionality is automatically called for the exterior ring, and for the interior ring collection. In the case of a point, boxes and segments, nothing will happen.

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

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

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

Either

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

Or

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

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

Point |
Nothing happens, geometry is unchanged |

Segment |
Nothing happens, geometry is unchanged |

Rectangle |
Nothing happens, geometry is unchanged |

Linestring |
Linestring is cleared |

Ring |
Ring is cleared |

Polygon |
The exterior ring is cleared and all interior rings are removed |

Multi Point |
Multi Point is cleared |

Multi Linestring |
Multi Linestring is cleared |

Multi Polygon |
Multi Polygon is cleared |

Constant

Shows how to clear a ring or polygon

#include <iostream> #include <boost/geometry.hpp> #include <boost/geometry/geometries/polygon.hpp> #include <boost/geometry/geometries/ring.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::tuple<float, float> point; typedef boost::geometry::model::polygon<point> polygon; typedef boost::geometry::model::ring<point> ring; polygon poly; // Fill the polygon (using its own methods + Boost.Assign) poly.outer() = tuple_list_of(0, 0)(0, 9)(10, 10)(0, 0); poly.inners().push_back(tuple_list_of(1, 2)(4, 6)(2, 8)(1, 2)); std::cout << boost::geometry::dsv(poly) << std::endl; boost::geometry::clear(poly); std::cout << boost::geometry::dsv(poly) << std::endl; // Create a ring using Boost.Assign ring r = tuple_list_of(0, 0)(0, 9)(8, 8)(0, 0); std::cout << boost::geometry::dsv(r) << std::endl; boost::geometry::clear(r); std::cout << boost::geometry::dsv(r) << std::endl; return 0; }

Output:

(((0, 0), (0, 10), (11, 11), (0, 0)), ((0, 0), (0, 10), (11, 11), (0, 0))) (()) ((0, 0), (0, 9), (8, 8), (0, 0)) ()