Calculate centroid of 2D non crossing polygon,

To accommodate that points are correct using Gift wrapping algorithm(Finding Convex Hull)

**Test case **

import static org.junit.Assert.assertEquals; import static org.junit.Assert.assertNotNull; import java.awt.Point; import java.util.ArrayList; import java.util.Arrays; import java.util.List; import org.junit.Test; public class MathUtilTest { @Test public void computeCentroidWithHull() { Point p1 = new Point(1, 1); Point p2 = new Point(2, 2); Point p3 = new Point(3, 1); Point p4 = new Point(1, 0); Point p5 = new Point(0, 1); Point p6 = new Point(5, 5); Point centroid2d = MathUtil.centroid2D(Arrays.asList(p1, p2, p3, p4, p5, p6)); assertEquals(new Point(2, 1), centroid2d); } @Test public void computeCentroid() { Point p1 = new Point(1, 1); Point p2 = new Point(2, 2); Point p3 = new Point(3, 1); Point centroid2d = MathUtil.centroid2D(Arrays.asList(p1, p2, p3)); assertEquals(new Point2D(2, 1), centroid2d); } } |

Implementation

/** * Calculate centroid of 2D non crossing polygon, To accommodate that points * are correct using Gift wrapping algorithm(Finding Convex Hull) * * @ref http://en.wikipedia.org/wiki/Centroid#Centroid_of_polygon * @param vertices * @return */ public static Point centroid2D(final List<Point> vertices) { if (vertices == null) return new Point(0, 0); List<Point> hull = null; if (vertices.size() < 2) hull = new ArrayList<Point>(vertices); else hull = findConvexHull(vertices); // Now we can calculate the centroid of polygon using standard mean final int len = hull.size(); final double xy[] = new double[] { 0, 0 }; for (int i = 0; i < len; ++i) { final Point p = hull.get(i); xy[0] += p.getX(); xy[1] += p.getY(); } final int x = (int) (xy[0] / len); final int y = (int) (xy[1] / len); return new Point(x, y); } |