/*
* Copyright (c) 2016 Martin Davis.
*
* 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 test.jts.perf.algorithm;
import org.locationtech.jts.geom.Coordinate;
import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.geom.GeometryFactory;
import org.locationtech.jts.geom.LinearRing;
import org.locationtech.jts.geom.Polygon;
public class AreaPrecisionPerfTest
{
public static void main(String[] args) throws Exception
{
double originX = 1000000;
double originY = 5000000;
long start = System.currentTimeMillis();
for (int nrVertices = 4; nrVertices <= 1000000; nrVertices *= 2) {
Coordinate[] coordinates = new Coordinate[nrVertices + 1];
Coordinate vertex;
for (int i = 0; i <= nrVertices; i++) {
vertex = new Coordinate(originX
+ (1 + Math.sin((float) i / (float) nrVertices * 2 * Math.PI)),
originY
+ (1 + Math.cos((float) i / (float) nrVertices * 2 * Math.PI)));
coordinates[i] = vertex;
}
// close ring
coordinates[nrVertices] = coordinates[0];
Geometry g1 = new GeometryFactory().createLinearRing(coordinates);
LinearRing[] holes = new LinearRing[] {};
Polygon polygon = (Polygon) new GeometryFactory().createPolygon(
(LinearRing) g1, holes);
System.out.println(polygon);
double area = originalSignedArea(coordinates);
double area2 = accurateSignedArea(coordinates);
double exactArea = 0.5 * nrVertices * Math.sin(2 * Math.PI / nrVertices);
double eps = exactArea - area;
double eps2 = exactArea - area2;
System.out.println(nrVertices + " orig err: " + eps
+ " acc err: " + eps2);
}
System.out.println("Time: " + (System.currentTimeMillis() - start) / 1000.0);
}
public static double originalSignedArea(Coordinate[] ring)
{
if (ring.length < 3)
return 0.0;
double sum = 0.0;
for (int i = 0; i < ring.length - 1; i++) {
double bx = ring[i].x;
double by = ring[i].y;
double cx = ring[i + 1].x;
double cy = ring[i + 1].y;
sum += (bx + cx) * (cy - by);
}
return -sum / 2.0;
}
public static double accurateSignedArea(Coordinate[] ring)
{
if (ring.length < 3)
return 0.0;
double sum = 0.0;
// http://en.wikipedia.org/wiki/Shoelace_formula
double x0 = ring[0].x;
for (int i = 1; i < ring.length - 1; i++) {
double x = ring[i].x - x0;
double y1 = ring[i + 1].y;
double y2 = ring[i == 0 ? ring.length - 1 : i - 1].y;
sum += x * (y2 - y1);
}
return sum / 2.0;
}
}