com.vividsolutions.jts.operation.overlay.validate.OffsetPointGenerator Maven / Gradle / Ivy
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/*
* The JTS Topology Suite is a collection of Java classes that
* implement the fundamental operations required to validate a given
* geo-spatial data set to a known topological specification.
*
* Copyright (C) 2001 Vivid Solutions
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* For more information, contact:
*
* Vivid Solutions
* Suite #1A
* 2328 Government Street
* Victoria BC V8T 5G5
* Canada
*
* (250)385-6040
* www.vividsolutions.com
*/
package com.vividsolutions.jts.operation.overlay.validate;
import java.util.*;
import com.vividsolutions.jts.geom.*;
import com.vividsolutions.jts.geom.util.*;
/**
* Generates points offset by a given distance
* from both sides of the midpoint of
* all segments in a {@link Geometry}.
* Can be used to generate probe points for
* determining whether a polygonal overlay result
* is incorrect.
* The input geometry may have any orientation for its rings,
* but {@link #setSidesToGenerate(boolean, boolean)} is
* only meaningful if the orientation is known.
*
* @author Martin Davis
* @version 1.7
*/
public class OffsetPointGenerator
{
private Geometry g;
private boolean doLeft = true;
private boolean doRight = true;
public OffsetPointGenerator(Geometry g)
{
this.g = g;
}
/**
* Set the sides on which to generate offset points.
*
* @param doLeft
* @param doRight
*/
public void setSidesToGenerate(boolean doLeft, boolean doRight)
{
this.doLeft = doLeft;
this.doRight = doRight;
}
/**
* Gets the computed offset points.
*
* @return List
*/
public List getPoints(double offsetDistance)
{
List offsetPts = new ArrayList();
List lines = LinearComponentExtracter.getLines(g);
for (Iterator i = lines.iterator(); i.hasNext(); ) {
LineString line = (LineString) i.next();
extractPoints(line, offsetDistance, offsetPts);
}
//System.out.println(toMultiPoint(offsetPts));
return offsetPts;
}
private void extractPoints(LineString line, double offsetDistance, List offsetPts)
{
Coordinate[] pts = line.getCoordinates();
for (int i = 0; i < pts.length - 1; i++) {
computeOffsetPoints(pts[i], pts[i + 1], offsetDistance, offsetPts);
}
}
/**
* Generates the two points which are offset from the
* midpoint of the segment (p0, p1) by the
* offsetDistance.
*
* @param p0 the first point of the segment to offset from
* @param p1 the second point of the segment to offset from
*/
private void computeOffsetPoints(Coordinate p0, Coordinate p1, double offsetDistance, List offsetPts)
{
double dx = p1.x - p0.x;
double dy = p1.y - p0.y;
double len = Math.sqrt(dx * dx + dy * dy);
// u is the vector that is the length of the offset, in the direction of the segment
double ux = offsetDistance * dx / len;
double uy = offsetDistance * dy / len;
double midX = (p1.x + p0.x) / 2;
double midY = (p1.y + p0.y) / 2;
if (doLeft) {
Coordinate offsetLeft = new Coordinate(midX - uy, midY + ux);
offsetPts.add(offsetLeft);
}
if (doRight) {
Coordinate offsetRight = new Coordinate(midX + uy, midY - ux);
offsetPts.add(offsetRight);
}
}
}