Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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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/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] 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

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