Boost C++ Libraries

Calculates the buffer of a geometry.

Description

The free function buffer calculates the buffer (a polygon being the spatial point set collection within a specified maximum distance from a geometry) of a geometry.

Synopsis

template<typename GeometryIn, typename GeometryOut, typename DistanceStrategy, typename SideStrategy,
         typename JoinStrategy, typename EndStrategy, typename PointStrategy>
void buffer(GeometryIn const & geometry_in, GeometryOut & geometry_out, DistanceStrategy const & distance_strategy,
            SideStrategy const & side_strategy, JoinStrategy const & join_strategy, EndStrategy const & end_strategy,
            PointStrategy const & point_strategy)

Parameters

Header

Either

#include <boost/geometry.hpp>

Or

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

Strategies

The 5 strategies give the user control to the generated buffer

By specifying a negative distance for the distance_strategy, for the (multi) polygon case, the polygon will be smaller (also known as deflate). The distance cannot be 0.

The next figure shows where in the generated buffer the strategies have effect

Conformance

The function buffer implements function Buffer from the OGC Simple Feature Specification.

It is conformant if used with the following combination of strategies: join_round, end_round, distance_symmetric, point_circle, side_straight

Supported geometries

Examples

Shows how the buffer algorithm can be used to create a buffer of a linestring, a multi point, a multi polygon

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


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

    // Declare strategies
    const double buffer_distance = 1.0;
    const int points_per_circle = 36;
    boost::geometry::strategy::buffer::distance_symmetric<coordinate_type> distance_strategy(buffer_distance);
    boost::geometry::strategy::buffer::join_round join_strategy(points_per_circle);
    boost::geometry::strategy::buffer::end_round end_strategy(points_per_circle);
    boost::geometry::strategy::buffer::point_circle circle_strategy(points_per_circle);
    boost::geometry::strategy::buffer::side_straight side_strategy;

    // Declare output
    boost::geometry::model::multi_polygon<polygon> result;

    // Declare/fill a linestring
    boost::geometry::model::linestring<point> ls;
    boost::geometry::read_wkt("LINESTRING(0 0,4 5,7 4,10 6)", ls);

    // Create the buffer of a linestring
    boost::geometry::buffer(ls, result,
                distance_strategy, side_strategy,
                join_strategy, end_strategy, circle_strategy);


    // Declare/fill a multi point
    boost::geometry::model::multi_point<point> mp;
    boost::geometry::read_wkt("MULTIPOINT((3 3),(4 4),(6 2))", mp);

    // Create the buffer of a multi point
    boost::geometry::buffer(mp, result,
                distance_strategy, side_strategy,
                join_strategy, end_strategy, circle_strategy);


    // Declare/fill a multi_polygon
    boost::geometry::model::multi_polygon<polygon> mpol;
    boost::geometry::read_wkt("MULTIPOLYGON(((0 1,2 5,5 3,0 1)),((1 1,5 2,5 0,1 1)))", mpol);

    // Create the buffer of a multi polygon
    boost::geometry::buffer(mpol, result,
                distance_strategy, side_strategy,
                join_strategy, end_strategy, circle_strategy);


    return 0;
}

The linestring case

The multi_point case

The multi_polygon case

Available Strategies