webringinspector.java

esri的ArcGIS Server超级学习模板程序（for java）

package com.esri.solutions.jitk.common.geometry;

import com.esri.adf.web.data.geometry.WebPoint;
import com.esri.adf.web.data.geometry.WebRing;

public class WebRingInspector {	
	protected WebRing _ring;
	
	/**
	 * Constructor
	 * @param ring {@link WebRing} converted to screen coordinates to be inspected
	 */
	public WebRingInspector(WebRing ring) {
		_ring = ring;
	}
	
	/**
	 * Returns true if the {@link WebRing} repeats the last vertex
	 * @return true if the {@link WebRing} repeats the last vertex
	 */
	public boolean isLastVertexRepeated() {
		WebPoint p1 = _ring.getPoints().get(0);
		WebPoint p2 = _ring.getPoints().get(_ring.getPoints().size() - 1);
		boolean isSame = false;
		
		if (p1.getX() == p2.getX()) {
			if (p1.getY() == p2.getY()) {
				isSame = true; 
			}
		}
		
		return isSame;
	}
	
	protected double inverse(double d) {
		return -1 * d;
	}
	
	/**
	 * Determines if the orientation of the passed {@Link WebRing} is clockwise.
	 * This method assumes the geometry has been converted to the screen coordinates,
	 * not geographically spatial coordinates.
	 * @return true if the orientation of the ring is clockwise
	 * @throws {@link InvalidWebGeometryException} if ring has less than 3 vertices
	 */
	public boolean isClockwise() throws InvalidWebGeometryException {
		//Algorithm ported from http://debian.fmi.uni-sofia.bg/~sergei/cgsr/docs/clockwise.htm
		
		if (_ring == null) {
			throw new NullPointerException("ring is null");
		}
		
		if (_ring.getPoints() == null) {
			throw new NullPointerException("ring point collection (list) is null");
		}
		
		double z;
		int count = 0;
		int vertexCount = _ring.getPoints().size();
		
		if (isLastVertexRepeated()) {
			vertexCount--;
		}

		if (vertexCount < 3) {
			throw new InvalidWebGeometryException("Ring has less than 3 vertices");
		} else {
			for (int vertexIndex = 0; vertexIndex < vertexCount; vertexIndex++) {
				int j = (vertexIndex + 1) % vertexCount;
				int k = (vertexIndex + 2) % vertexCount;
				WebPoint vertexJ = _ring.getPoints().get(j);
				WebPoint vertexK = _ring.getPoints().get(k);
				WebPoint vertexI = _ring.getPoints().get(vertexIndex);
				
				z  = (vertexJ.getX() - vertexI.getX()) * (inverse(vertexK.getY()) - inverse(vertexJ.getY()));
				z -= (inverse(vertexJ.getY()) - inverse(vertexI.getY())) * (vertexK.getX() - vertexJ.getX());
				
				if (z < 0) {
					count--;
				} else if (z > 0) {
					count++;
				}
			}
			
			if (count > 0) {
				return false;
			} else if (count < 0) {
				return true;
			} else {
				throw new InvalidWebGeometryException("Clockwise orientation of ring could not be determined");
			}
		}
	}
}