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##### line_interpolate

Returns one or more points interpolated along a LineString.

###### Synopsis

    template<typename Geometry, typename Distance, typename Pointlike>
    void line_interpolate(Geometry const & geometry, Distance const & max_distance, Pointlike & pointlike)

###### Parameters

Type | Concept | Name | Description
--- | --- | --- | ---
Geometry const & | Any type fulfilling a LineString concept | geometry | Input geometry
Distance const & | A numerical distance measure | max_distance | Distance threshold (in units depending on coordinate system) representing the spacing between the points
Pointlike & | Any type fulfilling Point or Multipoint concept | pointlike | Output: either a Point (exactly one point will be constructed) or a MultiPoint (depending on the max_distance one or more points will be constructed)

###### Header

Either

`#include <boost/geometry.hpp>`

Or

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

###### Conformance

The function line_interpolate_point is not defined by OGC.

| Note
PostGIS contains an algorithm ST_LineInterpolatePoints with similar functionality. See the PostGIS documentation.

###### Behavior

The algorithm iterates among segments of the linestring and computes interpolation points if needed.

###### Example

Shows how to interpolate points on a linestring

    #include <iostream>

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

    using namespace boost::geometry;

    int main()
    {
        typedef boost::geometry::model::d2::point_xy<double> point_type;
        using segment_type = model::segment<point_type>;
        using linestring_type = model::linestring<point_type>;
        using multipoint_type = model::multi_point<point_type>;

        segment_type const s { {0, 0}, {1, 1} };
        linestring_type const l { {0, 0}, {1, 0}, {1, 1}, {0, 1}, {0, 2} };
        point_type p;
        multipoint_type mp;

        std::cout << "point interpolation" << std::endl;

        line_interpolate(s, std::sqrt(2)/4, p);
        std::cout << "on segment : " << wkt(p) << std::endl;

        line_interpolate(l, 1.4, p);
        std::cout << "on linestring : " << wkt(p) << std::endl << std::endl;

        std::cout << "multipoint interpolation" << std::endl;

        line_interpolate(s, std::sqrt(2)/4, mp);
        std::cout << "on segment : " << wkt(mp) << std::endl;

        mp=multipoint_type();
        line_interpolate(l, 1.4, mp);
        std::cout << "on linestring : " << wkt(mp) << std::endl;

        return 0;
    }

Output:

    point interpolation
    on segment : POINT(0.25 0.25)
    on linestring : POINT(1 0.4)

    multipoint interpolation
    on segment : MULTIPOINT((0.25 0.25),(0.5 0.5),(0.75 0.75),(1 1))
    on linestring : MULTIPOINT((1 0.4),(0.2 1))

###### See also

- densify