clear

Clears a linestring, ring or polygon (exterior+interiors) or multi*.

Generic function to clear a geometry. All points will be removed from the collection or collections making up the geometry. In most cases this is equivalent to the .clear() method of a std::vector<...>. In the case of a polygon, this clear functionality is automatically called for the exterior ring, and for the interior ring collection. In the case of a point, boxes and segments, nothing will happen.

Synopsis

template<typename Geometry>
void clear(Geometry & geometry)

Parameters

Type	Concept	Name	Description
Geometry &	Any type fulfilling a Geometry Concept	geometry	A model of the specified concept which will be cleared

Header

Either

#include <boost/geometry.hpp>

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

Conformance

The function clear is not defined by OGC.

The function clear conforms to the clear() method of the C++ std-library.

Supported geometries

Geometry	Status
Point
Segment
Box
Linestring
Ring
Polygon
MultiPoint
MultiLinestring
MultiPolygon
Variant

Behavior

Case	Behavior
Point	Nothing happens, geometry is unchanged
Segment	Nothing happens, geometry is unchanged
Box	Nothing happens, geometry is unchanged
Linestring	Linestring is cleared
Ring	Ring is cleared
Polygon	The exterior ring is cleared and all interior rings are removed
Multi Point	Multi Point is cleared
Multi Linestring	Multi Linestring is cleared
Multi Polygon	Multi Polygon is cleared

Complexity

Constant

Example

Shows how to clear 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<float, float> point;
    typedef boost::geometry::model::polygon<point> polygon;
    typedef boost::geometry::model::ring<point> ring;

    polygon poly;

    // Fill the polygon (using its own methods + Boost.Assign)
    poly.outer() = tuple_list_of(0, 0)(0, 9)(10, 10)(0, 0);
    poly.inners().push_back(tuple_list_of(1, 2)(4, 6)(2, 8)(1, 2));

    std::cout << boost::geometry::dsv(poly) << std::endl;
    boost::geometry::clear(poly);
    std::cout << boost::geometry::dsv(poly) << std::endl;

    // Create a ring using Boost.Assign
    ring r = tuple_list_of(0, 0)(0, 9)(8, 8)(0, 0);

    std::cout << boost::geometry::dsv(r) << std::endl;
    boost::geometry::clear(r);
    std::cout << boost::geometry::dsv(r) << std::endl;

    return 0;
}

Output:

(((0, 0), (0, 10), (11, 11), (0, 0)), ((0, 0), (0, 10), (11, 11), (0, 0)))
(())
((0, 0), (0, 9), (8, 8), (0, 0))
()