原文地址:http://blog.163.com/kangle0925@126/blog/static/27758198201181484115912/
import java.util.ArrayList; /** * 判断一个点,是否在一个多边形区域内 */ public class Test { public static void main ( String[] args ) { double px = 113.705835; double py = 34.787479; ArrayList<Double> polygonXA = new ArrayList<Double>(); ArrayList<Double> polygonYA = new ArrayList<Double>(); polygonXA.add(113.700213);// 北京 polygonXA.add(113.706651);// 石家庄 polygonXA.add(113.706608);// 德州 polygonXA.add(113.707337);// 天津 polygonXA.add(113.701587);// 烟台 polygonXA.add(113.700128);// 唐山jdal polygonYA.add(34.791532); polygonYA.add(34.791568); polygonYA.add(34.789242); polygonYA.add(34.786633); polygonYA.add(34.786669); polygonYA.add(34.789242); Test test = new Test(); System.out.println(test.isPointInPolygon(px, py, polygonXA, polygonYA)); } public boolean isPointInPolygon ( double px , double py , ArrayList<Double> polygonXA , ArrayList<Double> polygonYA ) { boolean isInside = false; double ESP = 1e-9; int count = 0; double linePoint1x; double linePoint1y; double linePoint2x = 180; double linePoint2y; linePoint1x = px; linePoint1y = py; linePoint2y = py; for (int i = 0; i < polygonXA.size() - 1; i++) { double cx1 = polygonXA.get(i); double cy1 = polygonYA.get(i); double cx2 = polygonXA.get(i + 1); double cy2 = polygonYA.get(i + 1); if ( isPointOnLine(px, py, cx1, cy1, cx2, cy2) ) { return true; } if ( Math.abs(cy2 - cy1) < ESP ) { continue; } if ( isPointOnLine(cx1, cy1, linePoint1x, linePoint1y, linePoint2x, linePoint2y) ) { if ( cy1 > cy2 ) count++; } else if ( isPointOnLine(cx2, cy2, linePoint1x, linePoint1y, linePoint2x, linePoint2y) ) { if ( cy2 > cy1 ) count++; } else if ( isIntersect(cx1, cy1, cx2, cy2, linePoint1x, linePoint1y, linePoint2x, linePoint2y) ) { count++; } } System.out.println(count); if ( count % 2 == 1 ) { isInside = true; } return isInside; } public double Multiply ( double px0 , double py0 , double px1 , double py1 , double px2 , double py2 ) { return ((px1 - px0) * (py2 - py0) - (px2 - px0) * (py1 - py0)); } public boolean isPointOnLine ( double px0 , double py0 , double px1 , double py1 , double px2 , double py2 ) { boolean flag = false; double ESP = 1e-9; if ( (Math.abs(Multiply(px0, py0, px1, py1, px2, py2)) < ESP) && ((px0 - px1) * (px0 - px2) <= 0) && ((py0 - py1) * (py0 - py2) <= 0) ) { flag = true; } return flag; } public boolean isIntersect ( double px1 , double py1 , double px2 , double py2 , double px3 , double py3 , double px4 , double py4 ) { boolean flag = false; double d = (px2 - px1) * (py4 - py3) - (py2 - py1) * (px4 - px3); if ( d != 0 ) { double r = ((py1 - py3) * (px4 - px3) - (px1 - px3) * (py4 - py3)) / d; double s = ((py1 - py3) * (px2 - px1) - (px1 - px3) * (py2 - py1)) / d; if ( (r >= 0) && (r <= 1) && (s >= 0) && (s <= 1) ) { flag = true; } } return flag; } }