/*
* Copyright (c) 2016 Vivid Solutions.
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
* and the Eclipse Distribution License is available at
*
* http://www.eclipse.org/org/documents/edl-v10.php.
*/
package org.locationtech.jts.simplify;
import org.locationtech.jts.geom.Coordinate;
import org.locationtech.jts.geom.CoordinateSequence;
import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.geom.LinearRing;
import org.locationtech.jts.geom.MultiPolygon;
import org.locationtech.jts.geom.Polygon;
import org.locationtech.jts.geom.util.GeometryTransformer;
/**
* Simplifies a {@link Geometry} using the Douglas-Peucker 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.
* <p>
* Note that in general D-P 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.
* To simplify geometry while preserving topology use {@link TopologyPreservingSimplifier}.
* (However, using D-P is significantly faster).
*<h2>KNOWN BUGS</h2>
*<ul>
*<li>In some cases the approach used to clean invalid simplified polygons
*can distort the output geometry severely.
*</ul>
*
*
* @version 1.7
* @see TopologyPreservingSimplifier
*/
public class DouglasPeuckerSimplifier
{
/**
* Simplifies a geometry using a given tolerance.
*
* @param geom geometry to simplify
* @param distanceTolerance the tolerance to use
* @return a simplified version of the geometry
*/
public static Geometry simplify(Geometry geom, double distanceTolerance)
{
DouglasPeuckerSimplifier tss = new DouglasPeuckerSimplifier(geom);
tss.setDistanceTolerance(distanceTolerance);
return tss.getResultGeometry();
}
private Geometry inputGeom;
private double distanceTolerance;
private boolean isEnsureValidTopology = true;
/**
* Creates a simplifier for a given geometry.
*
* @param inputGeom the geometry to simplify
*/
public DouglasPeuckerSimplifier(Geometry inputGeom)
{
this.inputGeom = inputGeom;
}
/**
* 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.
*
* @param distanceTolerance the approximation tolerance to use
*/
public void setDistanceTolerance(double distanceTolerance) {
if (distanceTolerance < 0.0)
throw new IllegalArgumentException("Tolerance must be non-negative");
this.distanceTolerance = distanceTolerance;
}
/**
* Controls whether simplified polygons will be "fixed"
* to have valid topology.
* The caller may choose to disable this because:
* <ul>
* <li>valid topology is not required
* <li>fixing topology is a relative expensive operation
* <li>in some pathological cases the topology fixing operation may either fail or run for too long
* </ul>
*
* The default is to fix polygon topology.
*
* @param isEnsureValidTopology
*/
public void setEnsureValid(boolean isEnsureValidTopology)
{
this.isEnsureValidTopology = isEnsureValidTopology;
}
/**
* Gets the simplified geometry.
*
* @return the simplified geometry
*/
public Geometry getResultGeometry()
{
// empty input produces an empty result
if (inputGeom.isEmpty()) return (Geometry) inputGeom.clone();
return (new DPTransformer(isEnsureValidTopology)).transform(inputGeom);
}
class DPTransformer
extends GeometryTransformer
{
private boolean isEnsureValidTopology = true;
public DPTransformer(boolean isEnsureValidTopology)
{
this.isEnsureValidTopology = isEnsureValidTopology;
}
protected CoordinateSequence transformCoordinates(CoordinateSequence coords, Geometry parent)
{
Coordinate[] inputPts = coords.toCoordinateArray();
Coordinate[] newPts = null;
if (inputPts.length == 0) {
newPts = new Coordinate[0];
}
else {
newPts = DouglasPeuckerLineSimplifier.simplify(inputPts, distanceTolerance);
}
return factory.getCoordinateSequenceFactory().create(newPts);
}
/**
* Simplifies a polygon, fixing it if required.
*/
protected Geometry transformPolygon(Polygon geom, Geometry parent) {
// empty geometries are simply removed
if (geom.isEmpty())
return null;
Geometry rawGeom = super.transformPolygon(geom, parent);
// don't try and correct if the parent is going to do this
if (parent instanceof MultiPolygon) {
return rawGeom;
}
return createValidArea(rawGeom);
}
/**
* Simplifies a LinearRing. If the simplification results
* in a degenerate ring, remove the component.
*
* @return null if the simplification results in a degenerate ring
*/
protected Geometry transformLinearRing(LinearRing geom, Geometry parent)
{
boolean removeDegenerateRings = parent instanceof Polygon;
Geometry simpResult = super.transformLinearRing(geom, parent);
if (removeDegenerateRings && ! (simpResult instanceof LinearRing))
return null;;
return simpResult;
}
/**
* Simplifies a MultiPolygon, fixing it if required.
*/
protected Geometry transformMultiPolygon(MultiPolygon geom, Geometry parent) {
Geometry rawGeom = super.transformMultiPolygon(geom, parent);
return createValidArea(rawGeom);
}
/**
* Creates a valid area geometry from one that possibly has
* bad topology (i.e. self-intersections).
* Since buffer can handle invalid topology, but always returns
* valid geometry, constructing a 0-width buffer "corrects" the
* topology.
* Note this only works for area geometries, since buffer always returns
* areas. This also may return empty geometries, if the input
* has no actual area.
*
* @param rawAreaGeom an area geometry possibly containing self-intersections
* @return a valid area geometry
*/
private Geometry createValidArea(Geometry rawAreaGeom)
{
if ( isEnsureValidTopology)
return rawAreaGeom.buffer(0.0);
return rawAreaGeom;
}
}
}