/*
* 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.algorithm;
import org.locationtech.jts.geom.Coordinate;
import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.geom.GeometryCollection;
import org.locationtech.jts.geom.Polygon;
/**
* Computes the centroid of an area geometry.
* <h2>Algorithm</h2>
* Based on the usual algorithm for calculating
* the centroid as a weighted sum of the centroids
* of a decomposition of the area into (possibly overlapping) triangles.
* The algorithm has been extended to handle holes and multi-polygons.
* See <code>http://www.faqs.org/faqs/graphics/algorithms-faq/</code>
* for further details of the basic approach.
* The code has also be extended to handle degenerate (zero-area) polygons.
* In this case, the centroid of the line segments in the polygon
* will be returned.
*
* @version 1.7
* @deprecated use Centroid instead
*/
public class CentroidArea
{
private Coordinate basePt = null;// the point all triangles are based at
private Coordinate triangleCent3 = new Coordinate();// temporary variable to hold centroid of triangle
private double areasum2 = 0; /* Partial area sum */
private Coordinate cg3 = new Coordinate(); // partial centroid sum
// data for linear centroid computation, if needed
private Coordinate centSum = new Coordinate();
private double totalLength = 0.0;
public CentroidArea()
{
basePt = null;
}
/**
* Adds the area defined by a Geometry to the centroid total.
* If the geometry has no area it does not contribute to the centroid.
*
* @param geom the geometry to add
*/
public void add(Geometry geom)
{
if (geom instanceof Polygon) {
Polygon poly = (Polygon) geom;
setBasePoint(poly.getExteriorRing().getCoordinateN(0));
add(poly);
}
else if (geom instanceof GeometryCollection) {
GeometryCollection gc = (GeometryCollection) geom;
for (int i = 0; i < gc.getNumGeometries(); i++) {
add(gc.getGeometryN(i));
}
}
}
/**
* Adds the area defined by an array of
* coordinates. The array must be a ring;
* i.e. end with the same coordinate as it starts with.
* @param ring an array of {@link Coordinate}s
*/
public void add(Coordinate[] ring)
{
setBasePoint(ring[0]);
addShell(ring);
}
public Coordinate getCentroid()
{
Coordinate cent = new Coordinate();
if (Math.abs(areasum2) > 0.0) {
cent.x = cg3.x / 3 / areasum2;
cent.y = cg3.y / 3 / areasum2;
}
else {
// if polygon was degenerate, compute linear centroid instead
cent.x = centSum.x / totalLength;
cent.y = centSum.y / totalLength;
}
return cent;
}
private void setBasePoint(Coordinate basePt)
{
if (this.basePt == null)
this.basePt = basePt;
}
private void add(Polygon poly)
{
addShell(poly.getExteriorRing().getCoordinates());
for (int i = 0; i < poly.getNumInteriorRing(); i++) {
addHole(poly.getInteriorRingN(i).getCoordinates());
}
}
private void addShell(Coordinate[] pts)
{
boolean isPositiveArea = ! CGAlgorithms.isCCW(pts);
for (int i = 0; i < pts.length - 1; i++) {
addTriangle(basePt, pts[i], pts[i+1], isPositiveArea);
}
addLinearSegments(pts);
}
private void addHole(Coordinate[] pts)
{
boolean isPositiveArea = CGAlgorithms.isCCW(pts);
for (int i = 0; i < pts.length - 1; i++) {
addTriangle(basePt, pts[i], pts[i+1], isPositiveArea);
}
addLinearSegments(pts);
}
private void addTriangle(Coordinate p0, Coordinate p1, Coordinate p2, boolean isPositiveArea)
{
double sign = (isPositiveArea) ? 1.0 : -1.0;
centroid3( p0, p1, p2, triangleCent3 );
double area2 = area2( p0, p1, p2 );
cg3.x += sign * area2 * triangleCent3.x;
cg3.y += sign * area2 * triangleCent3.y;
areasum2 += sign * area2;
}
/**
* Returns three times the centroid of the triangle p1-p2-p3.
* The factor of 3 is
* left in to permit division to be avoided until later.
*/
private static void centroid3( Coordinate p1, Coordinate p2, Coordinate p3, Coordinate c )
{
c.x = p1.x + p2.x + p3.x;
c.y = p1.y + p2.y + p3.y;
return;
}
/**
* Returns twice the signed area of the triangle p1-p2-p3,
* positive if a,b,c are oriented ccw, and negative if cw.
*/
private static double area2( Coordinate p1, Coordinate p2, Coordinate p3 )
{
return
(p2.x - p1.x) * (p3.y - p1.y) -
(p3.x - p1.x) * (p2.y - p1.y);
}
/**
* Adds the linear segments defined by an array of coordinates
* to the linear centroid accumulators.
* This is done in case the polygon(s) have zero-area,
* in which case the linear centroid is computed instead.
*
* @param pts an array of {@link Coordinate}s
*/
private void addLinearSegments(Coordinate[] pts)
{
for (int i = 0; i < pts.length - 1; i++) {
double segmentLen = pts[i].distance(pts[i + 1]);
totalLength += segmentLen;
double midx = (pts[i].x + pts[i + 1].x) / 2;
centSum.x += segmentLen * midx;
double midy = (pts[i].y + pts[i + 1].y) / 2;
centSum.y += segmentLen * midy;
}
}
}