Boost C++ Libraries

Checks if a geometry are spatially equal.

Description

The free function equals checks if the first geometry is spatially equal the second geometry. Spatially equal means that the same point set is included. A box can therefore be spatially equal to a ring or a polygon, or a linestring can be spatially equal to a multi-linestring or a segment. This only works theoretically, not all combinations are implemented yet.

Synopsis

template<typename Geometry1, typename Geometry2>
bool equals(Geometry1 const & geometry1, Geometry2 const & geometry2)

Parameters

Returns

Returns true if two geometries are spatially equal

Header

Either

#include <boost/geometry.hpp>

Or

#include <boost/geometry/algorithms/equals.hpp>

Conformance

The function equals implements function Equals from the OGC Simple Feature Specification.

Supported geometries

Complexity

Linear

Example

Shows the predicate equals, which returns true if two geometries are spatially equal

#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::tuple<int, int> point;

    boost::geometry::model::polygon<point> poly1, poly2;
    boost::geometry::exterior_ring(poly1) = tuple_list_of(0, 0)(0, 5)(5, 5)(5, 0)(0, 0);
    boost::geometry::exterior_ring(poly2) = tuple_list_of(5, 0)(0, 0)(0, 5)(5, 5)(5, 0);

    std::cout
        << "polygons are spatially "
        << (boost::geometry::equals(poly1, poly2) ? "equal" : "not equal")
        << std::endl;

    boost::geometry::model::box<point> box;
    boost::geometry::assign_values(box, 0, 0, 5, 5);

    std::cout
        << "polygon and box are spatially "
        << (boost::geometry::equals(box, poly2) ? "equal" : "not equal")
        << std::endl;


    return 0;
}

Output:

polygons are spatially equal
polygon and box are spatially equal