Class CascadedPolygonUnion

java.lang.Object

org.locationtech.jts.operation.union.CascadedPolygonUnion

public class CascadedPolygonUnion
extends Object

Provides an efficient method of unioning a collection of Polygonal geometries. The geometries are indexed using a spatial index, and unioned recursively in index order. For geometries with a high degree of overlap, this has the effect of reducing the number of vertices early in the process, which increases speed and robustness.

This algorithm is faster and 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 a 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 situation for using buffer(0) is the trivial case where there is no overlap between the input geometries. However, this case is likely rare in practice.

Author:

Martin Davis

Constructor Summary

Constructors

Constructor	Description
CascadedPolygonUnion(Collection polys)	Creates a new instance to union the given collection of Geometrys.
CascadedPolygonUnion(Collection polys, UnionStrategy unionFun)	Creates a new instance to union the given collection of Geometrys.

Method Summary

Modifier and Type	Method	Description
Geometry	union()	Computes the union of the input geometries.
static Geometry	union(Collection polys)	Computes the union of a collection of Polygonal Geometrys.
static Geometry	union(Collection polys, UnionStrategy unionFun)	Computes the union of a collection of Polygonal Geometrys.

Methods inherited from class Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

CascadedPolygonUnion

public CascadedPolygonUnion(Collection polys)

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

Parameters:

polys - a collection of Polygonal Geometrys

CascadedPolygonUnion

public CascadedPolygonUnion(Collection polys,
 UnionStrategy unionFun)

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

Parameters:

polys - a collection of Polygonal Geometrys

Method Details

union

public static Geometry union(Collection polys)

Computes the union of a collection of Polygonal Geometrys.

Parameters:

polys - a collection of Polygonal Geometrys

union

public static Geometry union(Collection polys,
 UnionStrategy unionFun)

Computes the union of a collection of Polygonal Geometrys.

Parameters:

polys - a collection of Polygonal Geometrys

union

public Geometry union()

Computes the union of the input geometries.

This method discards the input geometries as they are processed. In many input cases this reduces the memory retained as the operation proceeds. Optimal memory usage is achieved by disposing of the original input collection before calling this method.

Returns:

the union of the input geometries or null if no input geometries were provided

Throws:

IllegalStateException - if this method is called more than once