reverse

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#### reverse

Reverses the points within a geometry.

###### Description

Generic function to reverse a geometry. It resembles the std::reverse functionality, but it takes the geometry type into account. Only for a ring or for a linestring it is the same as the std::reverse.

###### Synopsis

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

###### Parameters

Type | Concept | Name | Description
--- | --- | --- | ---
Geometry & | Any type fulfilling a Geometry Concept | geometry | A model of the specified concept which will be reversed

###### Header

Either

`#include <boost/geometry.hpp>`

Or

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

###### Conformance

The function reverse is not defined by OGC.

The function reverse conforms to the std::reverse function of the C++ std-library.

###### Behavior

Case | Behavior
--- | ---
Point | Nothing happens, geometry is unchanged
Segment | Not yet supported in this version
Box | Nothing happens, geometry is unchanged
Linestring | Reverses the Linestring
Ring | Reverses the Ring
Polygon | Reverses the exterior ring and all interior rings in the polygon
Multi Point | Nothing happens, geometry is unchanged
Multi Linestring | Reverses all contained linestrings individually
Multi Polygon | Reverses all contained polygons individually

| Note
The reverse of a (multi)polygon or ring might make a valid geometry invalid because the (counter)clockwise orientation reverses.

###### Complexity

Linear

###### Example

Shows how to reverse 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<int, int> point;
        typedef boost::geometry::model::polygon<point> polygon;
        typedef boost::geometry::model::ring<point> ring;

        polygon poly;
        boost::geometry::exterior_ring(poly) = tuple_list_of(0, 0)(0, 9)(10, 10)(0, 0);
        boost::geometry::interior_rings(poly).push_back(tuple_list_of(1, 2)(4, 6)(2, 8)(1, 2));

        double area_before = boost::geometry::area(poly);
        boost::geometry::reverse(poly);
        double area_after = boost::geometry::area(poly);
        std::cout << boost::geometry::dsv(poly) << std::endl;
        std::cout << area_before << " -> " << area_after << std::endl;

        ring r = tuple_list_of(0, 0)(0, 9)(8, 8)(0, 0);

        area_before = boost::geometry::area(r);
        boost::geometry::reverse(r);
        area_after = boost::geometry::area(r);
        std::cout << boost::geometry::dsv(r) << std::endl;
        std::cout << area_before << " -> " << area_after << std::endl;

        return 0;
    }

Output:

    (((0, 0), (10, 10), (0, 9), (0, 0)), ((1, 2), (2, 8), (4, 6), (1, 2)))
    38 -> -38
    ((0, 0), (8, 8), (0, 9), (0, 0))
    36 -> -36