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

#include <CascadedPolygonUnion.h>

Collaboration diagram for geos::operation::geounion::CascadedPolygonUnion:

Public Member Functions
	CascadedPolygonUnion ()

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

	CascadedPolygonUnion (std::vector< geom::Polygon * > polys, UnionStrategy unionFun)

geom::Geometry *	Union ()
	Computes the union of the input geometries. More...

Static Public Member Functions
static geom::Geometry *	Union (std::vector< geom::Polygon * > *polys)
	Computes the union of a collection of polygonal Geometrys. More...

static geom::Geometry *	Union (std::vector< geom::Polygon * > polys, UnionStrategy unionFun)

template<class T >
static geom::Geometry *	Union (T start, T end, UnionStrategy *unionStrategy)
	Computes the union of a set of polygonal Geometrys. More...

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

Private Member Functions
geom::Geometry *	unionTree (index::strtree::ItemsList *geomTree)

geom::Geometry *	binaryUnion (GeometryListHolder *geoms)

geom::Geometry *	binaryUnion (GeometryListHolder *geoms, std::size_t start, std::size_t end)

GeometryListHolder *	reduceToGeometries (index::strtree::ItemsList *geomTree)

geom::Geometry *	unionSafe (geom::Geometry g0, geom::Geometry g1)

geom::Geometry *	unionActual (geom::Geometry g0, geom::Geometry g1)

Static Private Member Functions
static std::unique_ptr< geom::Geometry >	restrictToPolygons (std::unique_ptr< geom::Geometry > g)
	Computes a Geometry containing only polygonal components. More...

Private Attributes
std::vector< geom::Polygon * > *	inputPolys

geom::GeometryFactory const *	geomFactory

UnionStrategy *	unionFunction

ClassicUnionStrategy	defaultUnionFunction

Static Private Attributes
static int const	STRTREE_NODE_CAPACITY = 4

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.

Definition at line 112 of file CascadedPolygonUnion.h.

Constructor & Destructor Documentation

geos::operation::geounion::CascadedPolygonUnion::CascadedPolygonUnion ( )

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

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.

Definition at line 189 of file CascadedPolygonUnion.h.

geos::operation::geounion::CascadedPolygonUnion::CascadedPolygonUnion	(	std::vector< geom::Polygon * > *	polys,
		UnionStrategy *	unionFun
	)

inline

Definition at line 195 of file CascadedPolygonUnion.h.

Member Function Documentation

geom::Geometry* geos::operation::geounion::CascadedPolygonUnion::binaryUnion ( GeometryListHolder * geoms )

private

Unions a list of geometries by treating the list as a flattened binary tree, and performing a cascaded union on the tree.

geom::Geometry* geos::operation::geounion::CascadedPolygonUnion::binaryUnion	(	GeometryListHolder *	geoms,
		std::size_t	start,
		std::size_t	end
	)

private

Unions a section of a list using a recursive binary union on each half of the section.

Parameters

geoms	the list of geometries containing the section to union
start	the start index of the section
end	the index after the end of the section

Returns: the union of the list section

GeometryListHolder* geos::operation::geounion::CascadedPolygonUnion::reduceToGeometries ( index::strtree::ItemsList * geomTree )

private

Reduces a tree of geometries to a list of geometries by recursively unioning the subtrees in the list.

Parameters

geomTree a tree-structured list of geometries

Returns: a list of Geometrys

static std::unique_ptr<geom::Geometry> geos::operation::geounion::CascadedPolygonUnion::restrictToPolygons ( std::unique_ptr< geom::Geometry > g )

staticprivate

Computes a Geometry containing only polygonal components.

Extracts the Polygons from the input and returns them as an appropriate polygonal geometry.

If the input is already Polygonal, it is returned unchanged.

A particular use case is to filter out non-polygonal components returned from an overlay operation.

Parameters

g	the geometry to filter

Returns: a Polygonal geometry

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.

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

static

template<class T >

static geom::Geometry* geos::operation::geounion::CascadedPolygonUnion::Union	(	T	start,
		T	end,
		UnionStrategy *	unionStrategy
	)

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
unionStrategy	strategy to apply

Definition at line 164 of file CascadedPolygonUnion.h.

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.

geom::Geometry* geos::operation::geounion::CascadedPolygonUnion::Union ( )

Computes the union of the input geometries.

Returns: the union of the input geometries; null if no input geometries were provided

geom::Geometry* geos::operation::geounion::CascadedPolygonUnion::unionActual	(	geom::Geometry *	g0,
		geom::Geometry *	g1
	)

private

Encapsulates the actual unioning of two polygonal geometries.

Parameters

g0
g1

Returns

geom::Geometry* geos::operation::geounion::CascadedPolygonUnion::unionSafe	(	geom::Geometry *	g0,
		geom::Geometry *	g1
	)

private

Computes the union of two geometries, either of both of which may be null.

Parameters

g0	a Geometry
g1	a Geometry

Returns: the union of the input(s); null if both inputs are null

geom::Geometry* geos::operation::geounion::CascadedPolygonUnion::unionTree ( index::strtree::ItemsList * geomTree )

private

Member Data Documentation

ClassicUnionStrategy geos::operation::geounion::CascadedPolygonUnion::defaultUnionFunction

private

Definition at line 212 of file CascadedPolygonUnion.h.

geom::GeometryFactory const* geos::operation::geounion::CascadedPolygonUnion::geomFactory

private

Definition at line 115 of file CascadedPolygonUnion.h.

std::vector<geom::Polygon*>* geos::operation::geounion::CascadedPolygonUnion::inputPolys

private

Definition at line 114 of file CascadedPolygonUnion.h.

int const geos::operation::geounion::CascadedPolygonUnion::STRTREE_NODE_CAPACITY = 4

staticprivate

The effectiveness of the index is somewhat sensitive to the node capacity. Testing indicates that a smaller capacity is better. For an STRtree, 4 is probably a good number (since this produces 2x2 "squares").

Definition at line 124 of file CascadedPolygonUnion.h.

UnionStrategy* geos::operation::geounion::CascadedPolygonUnion::unionFunction

private

Definition at line 211 of file CascadedPolygonUnion.h.

The documentation for this class was generated from the following file:

CascadedPolygonUnion.h

Public Member Functions

Static Public Member Functions

Private Member Functions

Static Private Member Functions

Private Attributes

Static Private Attributes

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation