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Checks if the first geometry is completely inside the second geometry.
The free function within checks if the first geometry is completely inside the second geometry.
template<typename Geometry1, typename Geometry2> bool within(Geometry1 const & geometry1, Geometry2 const & geometry2)
| Type | Concept | Name | Description | 
|---|---|---|---|
| Geometry1 const & | Any type fulfilling a Geometry Concept | geometry1 | A model of the specified concept which might be within the second geometry | 
| Geometry2 const & | Any type fulfilling a Geometry Concept | geometry2 | A model of the specified concept which might contain the first geometry | 
true if geometry1 is completely contained within geometry2, else false
Either
            #include <boost/geometry.hpp>
          
Or
            #include <boost/geometry/algorithms/within.hpp>
          
The function within implements function Within from the OGC Simple Feature Specification.
| ![[Note]](../../../../../../../../doc/src/images/note.png) | Note | 
|---|---|
| OGC defines within as completely within and not on the border. See the notes for within / on the border | 
| Point | Segment | Box | Linestring | Ring | Polygon | MultiPoint | MultiLinestring | MultiPolygon | Variant | |
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| Box | 
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| Linestring | 
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| Ring | 
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| Polygon | 
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| MultiPoint | 
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| MultiLinestring | 
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| MultiPolygon | 
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| Variant | 
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| ![[Note]](../../../../../../../../doc/src/images/note.png) | Note | 
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| In this status matrix above: columns are types of first parameter and rows are types of second parameter. So a point can be checked to be within a polygon, but not vice versa. | 
If a point is located exactly on the border of a geometry, the result depends on the strategy. The default strategy (Winding (coordinate system agnostic)) returns false in that case.
If a polygon has a reverse oriented (e.g. counterclockwise for a clockwise typed polygon), the result also depends on the strategy. The default strategy returns still true if a point is completely within the reversed polygon. There is a specific strategy which returns false in this case.
Linear
Shows how to detect if a point is inside a polygon, or not
#include <iostream> #include <list> #include <boost/geometry.hpp> #include <boost/geometry/geometries/point_xy.hpp> #include <boost/geometry/geometries/polygon.hpp> int main() { typedef boost::geometry::model::d2::point_xy<double> point_type; typedef boost::geometry::model::polygon<point_type> polygon_type; polygon_type poly; 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))", poly); point_type p(4, 1); std::cout << "within: " << (boost::geometry::within(p, poly) ? "yes" : "no") << std::endl; return 0; }
Output:
within: yes