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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comparable_distance

Calculate the comparable distance measurement of two geometries.

Description

The free function comparable_distance does not necessarily calculate the distance, but it calculates a distance measure such that two distances are comparable to each other. For example: for the Cartesian coordinate system, Pythagoras is used but the square root is not taken, which makes it faster and the results of two point pairs can still be compared to each other.

Synopsis

template<typename Geometry1, typename Geometry2>
default_distance_result<Geometry1, Geometry2>::type comparable_distance(Geometry1 const & geometry1, Geometry2 const & geometry2)

Parameters

Type

Concept

Name

Description

Geometry1 const &

first geometry type

geometry1

A model of the specified concept

Geometry2 const &

second geometry type

geometry2

A model of the specified concept

Returns

The calculated comparable distance

Header

Either

#include <boost/geometry/geometry.hpp>

Or

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

Conformance

The function comparable_distance is not defined by OGC.

Behaviour

There is no (not yet) version with a strategy.

It depends on the coordinate system of the geometry's point type if there is a strategy available which can determine (more efficient than the standard strategy) a measure of comparable distance.

Complexity

Linear

Example

Shows how to efficiently get the closest point

#include <iostream>

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>

#include <boost/numeric/conversion/bounds.hpp>
#include <boost/foreach.hpp>

int main()
{
    typedef boost::geometry::model::d2::point_xy<double> point_type;

    point_type p(1.4, 2.6);

    std::vector<point_type> v;
    for (double x = 0.0; x <= 4.0; x++)
    {
        for (double y = 0.0; y <= 4.0; y++)
        {
            v.push_back(point_type(x, y));
        }
    }

    point_type min_p;
    double min_d = boost::numeric::bounds<double>::highest();
    BOOST_FOREACH(point_type const& pv, v)
    {
        double d = boost::geometry::comparable_distance(p, pv);
        if (d < min_d)
        {
            min_d = d;
            min_p = pv;
        }
    }

    std::cout
        << "Closest: " << boost::geometry::dsv(min_p) << std::endl
        << "At: " << boost::geometry::distance(p, min_p) << std::endl;

    return 0;
}

Output:

Closest: (1, 3)
At: 0.565685

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