GEOS  3.9.0dev

Provides an efficient method of unioning a collection of polygonal geometries. More...

`#include <CascadedPolygonUnion.h>`

## Public Member Functions

CascadedPolygonUnion (std::vector< geom::Polygon * > *polys)
Creates a new instance to union the given collection of Geometrys. More...

geom::GeometryUnion ()
Computes the union of the input geometries. More...

## Static Public Member Functions

static geom::GeometryUnion (std::vector< geom::Polygon * > *polys)
Computes the union of a collection of polygonal Geometrys. More...

template<class T >
static geom::GeometryUnion (T start, T end)
Computes the union of a set of polygonal Geometrys. More...

static geom::GeometryUnion (const geom::MultiPolygon *polys)
Computes the union of a collection of polygonal Geometrys. More...

## Detailed Description

Provides an efficient method of unioning a collection of polygonal geometries.

This algorithm is faster and likely more robust than the simple iterated approach of repeatedly unioning each polygon to a result geometry.

The `buffer(0)` trick is sometimes faster, but can be less robust and can sometimes take an exceptionally long time to complete. This is particularly the case where there is a high degree of overlap between the polygons. In this case, `buffer(0)` is forced to compute with all line segments from the outset, whereas cascading can eliminate many segments at each stage of processing. The best case for buffer(0) is the trivial case where there is `no` overlap between the input geometries. However, this case is likely rare in practice.

## Constructor & Destructor Documentation

inline

Creates a new instance to union the given collection of Geometrys.

Parameters
 polys a collection of polygonal Geometrys. Ownership of elements and vector are left to caller.

## Member Function Documentation

 static geom::Geometry* geos::operation::geounion::CascadedPolygonUnion::Union ( std::vector< geom::Polygon * > * polys )
static

Computes the union of a collection of polygonal Geometrys.

Parameters
 polys a collection of polygonal Geometrys. ownership of elements and vector are left to caller.
template<class T >
 static geom::Geometry* geos::operation::geounion::CascadedPolygonUnion::Union ( T start, T end )
inlinestatic

Computes the union of a set of polygonal Geometrys.

Template Parameters
 T an iterator yelding something castable to const Polygon *
Parameters
 start start iterator end end iterator
 static geom::Geometry* geos::operation::geounion::CascadedPolygonUnion::Union ( const geom::MultiPolygon * polys )
static

Computes the union of a collection of polygonal Geometrys.

Parameters
 polys a collection of polygonal Geometrys. Ownership of elements and vector are left to caller.
`null` if no input geometries were provided