判断点是否在面内(java版).doc

import java.util.ArrayList;import java.util.List;/* * * * 2012-5-25下午4:37:31 */public class SystemTaskJob double INFINITY = 1e10; double ESP = 1e-5; int MAX_N = 1000;List Polygon;/ 计算叉乘 |P0P1| |P0P2|double Multiply(Point p1, Point p2, Point p0) return ( (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y) );/ 判断线段是否包含点pointprivate boolean IsOnline(Point point, LineSegment line) return( ( Math.abs(Multiply(line.pt1, line.pt2, point) ESP ) & ( ( point.x - line.pt1.x ) * ( point.x - line.pt2.x ) = 0 ) & ( ( point.y - line.pt1.y ) * ( point.y - line.pt2.y ) = Math.min(L2.pt1.x, L2.pt2.x) & (Math.max(L2.pt1.x, L2.pt2.x) = Math.min(L1.pt1.x, L1.pt2.x) & (Math.max(L1.pt1.y, L1.pt2.y) = Math.min(L2.pt1.y, L2.pt2.y) & (Math.max(L2.pt1.y, L2.pt2.y) = Math.min(L1.pt1.y, L1.pt2.y) & (Multiply(L2.pt1, L1.pt2, L1.pt1) * Multiply(L1.pt2, L2.pt2, L1.pt1) = 0) & (Multiply(L1.pt1, L2.pt2, L2.pt1) * Multiply(L2.pt2, L1.pt2, L2.pt1) = 0) );/* 射线法判断点q与多边形polygon的位置关系，要求polygon为简单多边形，顶点逆时针排列如果点在多边形内： 返回0如果点在多边形边上： 返回1如果点在多边形外： 返回2*/public int InPolygon(List polygon, Point point)int n = polygon.size(); int count = 0; LineSegment line = new LineSegment(); line.pt1 = point; line.pt2.y = point.y; line.pt2.x = - INFINITY; for( int i = 0; i n; i+ ) / 得到多边形的一条边 LineSegment side = new LineSegment(); side.pt1 = polygon.get(i); side.pt2 = polygon.get(i + 1) % n); if( IsOnline(point, side) ) return 1 ; / 如果side平行x轴则不作考虑 if( Math.abs(side.pt1.y - side.pt2.y) side.pt2.y ) count+; else if( IsOnline(side.pt2, line) ) if( side.pt2.y side.pt1.y ) count+; else if( Intersect(line, side) ) count+; if ( count % 2 = 1 ) return 0; else return 2; public static void main(String args) SystemTaskJob systemTaskJob = new SystemTaskJob(); List polygon = new ArrayList(); Point point1 = new Point(4,9); Point point2 = new Point(7,10); Point point3 = new Point(8,2); Point point4 = new Point(6,8); Point point5 = new Point(6,9); Point checkpoint = new Point(7,11); polygon.add(point1); polygon.add(point2); polygon.add(point3); polygon.add(point4); polygon.add(point5); int m = systemTaskJob.InPolygon(polygon, checkpoint); System.out.println(=+m); class Point public double x; public double y; public Point() public Point(double x,double y) this.x=x; this.y=y; class