org.locationtech.jts.simplify

Class VWSimplifier

java.lang.Object

org.locationtech.jts.simplify.VWSimplifier

public class VWSimplifier
extends Object

Simplifies a Geometry using the Visvalingam-Whyatt area-based algorithm. Ensures that any polygonal geometries returned are valid. Simple lines are not guaranteed to remain simple after simplification. All geometry types are handled. Empty and point geometries are returned unchanged. Empty geometry components are deleted.

The simplification tolerance is specified as a distance. This is converted to an area tolerance by squaring it.

Note that in general this algorithm does not preserve topology - e.g. polygons can be split, collapse to lines or disappear holes can be created or disappear, and lines can cross.

Known Bugs

• Not yet optimized for performance
• Does not simplify the endpoint of rings

To Do

• Allow specifying desired number of vertices in the output

Version:

1.7

Constructor Summary

Constructors

Constructor and Description
VWSimplifier(Geometry inputGeom) Creates a simplifier for a given geometry.

Method Summary

Modifier and Type	Method and Description
Geometry	getResultGeometry() Gets the simplified geometry.
void	setDistanceTolerance(double distanceTolerance) Sets the distance tolerance for the simplification.
void	setEnsureValid(boolean isEnsureValidTopology) Controls whether simplified polygons will be "fixed" to have valid topology.
static Geometry	simplify(Geometry geom, double distanceTolerance) Simplifies a geometry using a given tolerance.

Methods inherited from class java.lang.Object

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

Constructor Detail

VWSimplifier

public VWSimplifier(Geometry inputGeom)

Creates a simplifier for a given geometry.

Parameters:

inputGeom - the geometry to simplify

Method Detail

simplify

public static Geometry simplify(Geometry geom,
                                double distanceTolerance)

Simplifies a geometry using a given tolerance.

Parameters:

geom - geometry to simplify

distanceTolerance - the tolerance to use

Returns:

a simplified version of the geometry

setDistanceTolerance

public void setDistanceTolerance(double distanceTolerance)

Sets the distance tolerance for the simplification. All vertices in the simplified geometry will be within this distance of the original geometry. The tolerance value must be non-negative.

Parameters:

distanceTolerance - the approximation tolerance to use

setEnsureValid

public void setEnsureValid(boolean isEnsureValidTopology)

Controls whether simplified polygons will be "fixed" to have valid topology. The caller may choose to disable this because:

• valid topology is not required
• fixing topology is a relative expensive operation
• in some pathological cases the topology fixing operation may either fail or run for too long

The default is to fix polygon topology.

Parameters:

isEnsureValidTopology -

getResultGeometry

public Geometry getResultGeometry()

Gets the simplified geometry.

Returns:

the simplified geometry