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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.
template<typename Geometry> void clear(Geometry & geometry)
| Type | Concept | Name | Description | 
|---|---|---|---|
| Geometry & | Any type fulfilling a Geometry Concept | geometry | A model of the specified concept which will be cleared | 
Either
          #include <boost/geometry.hpp>
        
Or
          #include <boost/geometry/algorithms/clear.hpp>
        
The function clear is not defined by OGC.
The function clear conforms to the clear() method of the C++ std-library.
| Geometry | Status | 
|---|---|
| Point | 
                     | 
| Segment | 
                     | 
| Box | 
                     | 
| Linestring | 
                     | 
| Ring | 
                     | 
| Polygon | 
                     | 
| MultiPoint | 
                     | 
| MultiLinestring | 
                     | 
| MultiPolygon | 
                     | 
| Variant | 
                     | 
| 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 | 
Constant
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)) ()