unique

Calculates the minimal set of a geometry.

Description

The free function unique calculates the minimal set (where duplicate consecutive points are removed) of a geometry.

Synopsis

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

Parameters

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

Header

Either

#include <boost/geometry.hpp>

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

Conformance

The function unique is not defined by OGC.

The function unique conforms to the std::unique function of the C++ std-library.

Behavior

Case	Behavior
Point	Nothing happens, geometry is unchanged
Segment	Nothing happens, geometry is unchanged
Box	Nothing happens, geometry is unchanged
Linestring	Removes all consecutive duplicate points
Ring	Removes all consecutive duplicate points
Polygon	Removes all consecutive duplicate points in all rings
Multi Point	Nothing happens, geometry is unchanged. Even if two equal points happen to be stored consecutively, they are kept
Multi Linestring	Removes all consecutive duplicate points in all contained linestrings
Multi Polygon	Removes all consecutive duplicate points in all contained polygons (all rings)

Complexity

Linear

Example

Shows how to make a so-called minimal set of a polygon by removing duplicate points

#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)

int main()
{
    boost::geometry::model::polygon<boost::tuple<double, double> > poly;
    boost::geometry::read_wkt("POLYGON((0 0,0 0,0 5,5 5,5 5,5 5,5 0,5 0,0 0,0 0,0 0,0 0))", poly);
    boost::geometry::unique(poly);
    std::cout << boost::geometry::wkt(poly) << std::endl;

    return 0;
}

Output:

POLYGON((0 0,0 5,5 5,5 0,0 0))