...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Calculate the difference of two geometries
The free function difference calculates the spatial set theoretic difference of two geometries.
template<typename Geometry1, typename Geometry2, typename Collection> void difference(Geometry1 const & geometry1, Geometry2 const & geometry2, Collection & output_collection)
Type |
Concept |
Name |
Description |
---|---|---|---|
Geometry1 const & |
Any type fulfilling a Geometry Concept |
geometry1 |
A model of the specified concept |
Geometry2 const & |
Any type fulfilling a Geometry Concept |
geometry2 |
A model of the specified concept |
Collection & |
output collection, either a multi-geometry, or a std::vector<Geometry> / std::deque<Geometry> etc |
output_collection |
the output collection |
Either
#include <boost/geometry.hpp>
Or
#include <boost/geometry/algorithms/difference.hpp>
The function difference implements function Difference from the OGC Simple Feature Specification.
Case |
Behavior |
---|---|
areal (e.g. polygon) |
All combinations of: box, ring, polygon, multi_polygon |
linear (e.g. linestring) / areal (e.g. polygon) |
A combinations of a (multi) linestring with a (multi) polygon results in a collection of linestrings |
linear (e.g. linestring) |
All combinations of: linestring, multi_linestring; results in a collection of linestrings |
pointlike (e.g. point) |
All combinations of: point, multi_point; results in a collection of points |
Other geometries |
Not yet supported in this version |
Spherical |
Not yet supported in this version |
Three dimensional |
Not yet supported in this version |
Note | |
---|---|
Check the Polygon Concept for the rules that polygon input for this algorithm should fulfill |
Shows how to subtract one polygon from another polygon
#include <iostream> #include <list> #include <boost/geometry.hpp> #include <boost/geometry/geometries/point_xy.hpp> #include <boost/geometry/geometries/polygon.hpp> #include <boost/foreach.hpp> int main() { typedef boost::geometry::model::polygon<boost::geometry::model::d2::point_xy<double> > polygon; polygon green, blue; boost::geometry::read_wkt( "POLYGON((2 1.3,2.4 1.7,2.8 1.8,3.4 1.2,3.7 1.6,3.4 2,4.1 3,5.3 2.6,5.4 1.2,4.9 0.8,2.9 0.7,2 1.3)" "(4.0 2.0, 4.2 1.4, 4.8 1.9, 4.4 2.2, 4.0 2.0))", green); boost::geometry::read_wkt( "POLYGON((4.0 -0.5 , 3.5 1.0 , 2.0 1.5 , 3.5 2.0 , 4.0 3.5 , 4.5 2.0 , 6.0 1.5 , 4.5 1.0 , 4.0 -0.5))", blue); std::list<polygon> output; boost::geometry::difference(green, blue, output); int i = 0; std::cout << "green - blue:" << std::endl; BOOST_FOREACH(polygon const& p, output) { std::cout << i++ << ": " << boost::geometry::area(p) << std::endl; } output.clear(); boost::geometry::difference(blue, green, output); i = 0; std::cout << "blue - green:" << std::endl; BOOST_FOREACH(polygon const& p, output) { std::cout << i++ << ": " << boost::geometry::area(p) << std::endl; } return 0; }
Output:
green - blue: 0: 0.02375 1: 0.542951 2: 0.0149697 3: 0.226855 4: 0.839424 blue - green: 0: 0.525154 1: 0.015 2: 0.181136 3: 0.128798 4: 0.340083 5: 0.307778