geos::operation::geounion::CascadedUnion Class Reference

Provides an efficient method of unioning a collection of Geometries. More...

#include <CascadedUnion.h>

Collaboration diagram for geos::operation::geounion::CascadedUnion:

Public Member Functions
	CascadedUnion ()
	CascadedUnion (const std::vector< geom::Geometry * > *geoms)
geom::Geometry *	Union ()

Static Public Member Functions
static geom::Geometry *	Union (std::vector< geom::Geometry * > *geoms)
template<class T >
static geom::Geometry *	Union (T start, T end)

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 *	unionOptimized (geom::Geometry *g0, geom::Geometry *g1)
geom::Geometry *	unionUsingEnvelopeIntersection (geom::Geometry *g0, geom::Geometry *g1, geom::Envelope const &common)
geom::Geometry *	extractByEnvelope (geom::Envelope const &env, geom::Geometry *geom, std::vector< const geom::Geometry * > &disjointGeoms)

Static Private Member Functions
static geom::Geometry *	unionActual (geom::Geometry *g0, geom::Geometry *g1)

Private Attributes
const std::vector< geom::Geometry * > *	inputGeoms
geom::GeometryFactory const *	geomFactory

Static Private Attributes
static int const	STRTREE_NODE_CAPACITY = 4

Detailed Description

Provides an efficient method of unioning a collection of Geometries.

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

Definition at line 55 of file CascadedUnion.h.

Constructor & Destructor Documentation

geos::operation::geounion::CascadedUnion::CascadedUnion

(

)

geos::operation::geounion::CascadedUnion::CascadedUnion ( const std::vector< geom::Geometry * > *  geoms )

inline

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

Parameters

geoms

a collection of geom::Geometrys. Ownership of elements and vector are left to caller.

Definition at line 106 of file CascadedUnion.h.

Member Function Documentation

geom::Geometry* geos::operation::geounion::CascadedUnion::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::CascadedUnion::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
start
end

Returns

the union of the list section

geom::Geometry* geos::operation::geounion::CascadedUnion::extractByEnvelope ( geom::Envelope const &  env, geom::Geometry *  geom, std::vector< const geom::Geometry * > &  disjointGeoms  )

private

GeometryListHolder* geos::operation::geounion::CascadedUnion::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 geom::Geometry* geos::operation::geounion::CascadedUnion::Union ( std::vector< geom::Geometry * > *  geoms )

static

Computes the union of a collection of geom::Geometrys.

Parameters

geoms

a collection of geom::Geometrys. ownership of elements and vector are left to caller.

template<class T >

static geom::Geometry* geos::operation::geounion::CascadedUnion::Union ( T  start, T  end  )

inlinestatic

Computes the union of a set of geom::Geometrys.

Template Parameters

T	an iterator yelding something castable to const Geometry *

Parameters

start	start iterator
end	end iterator

Definition at line 89 of file CascadedUnion.h.

geom::Geometry* geos::operation::geounion::CascadedUnion::Union

(

)

Computes the union of the input geometries.

Returns

the union of the input geometries

null if no input geometries were provided

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

staticprivate

Encapsulates the actual unioning of two polygonal geometries.

Parameters

g0
g1

Returns

geom::Geometry* geos::operation::geounion::CascadedUnion::unionOptimized ( geom::Geometry *  g0, geom::Geometry *  g1  )

private

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

private

geom::Geometry* geos::operation::geounion::CascadedUnion::unionUsingEnvelopeIntersection ( geom::Geometry *  g0, geom::Geometry *  g1, geom::Envelope const &  common  )

private

Unions two geometries. The case of multi geometries is optimized to union only the components which lie in the intersection of the two geometry's envelopes. Geometrys outside this region can simply be combined with the union result, which is potentially much faster. This case is likely to occur often during cascaded union, and may also occur in real world data (such as unioning data for parcels on different street blocks).

Parameters

g0	a geometry
g1	a geometry
common	the intersection of the envelopes of the inputs

Returns

the union of the inputs

Member Data Documentation

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

private

Definition at line 58 of file CascadedUnion.h.

const std::vector<geom::Geometry*>* geos::operation::geounion::CascadedUnion::inputGeoms

private

Definition at line 57 of file CascadedUnion.h.

int const geos::operation::geounion::CascadedUnion::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 67 of file CascadedUnion.h.

---

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

• CascadedUnion.h