方法一：引射线法
就是从该点出发引一条射线，看这条射线和所有边的交点数目。如果有奇数个交点，则说明在内部，如果有偶数个交点，则说明在外部。这是所有方法中计算量最小的方法，在光线追踪算法中有大量的应用。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace 判断点是否在多边形内
{
class Program
{
public static void Main(String[] args)
{
Point[] ps = new Point[] { new Point(120.2043, 30.2795), new Point(120.2030, 30.2511), new Point(120.1810, 30.2543), new Point(120.1798, 30.2781), new Point(120.1926, 30.2752) };
Point n1 = new Point(120.1936, 30.2846);
Point n2 = new Point(120.1823, 30.2863);
Point n3 = new Point(120.2189, 30.2712);
Point y1 = new Point(120.1902, 30.2712);
Point y2 = new Point(120.1866, 30.2672);
Point y4 = new Point(120.1869, 30.2718);
Console.WriteLine(IsPtInPoly(120.2043, 30.2795, ps));
Console.ReadLine();
}
/// <summary>
/// 判断点是否在多边形内或多边形上
/// </summary>
/// <param name="ALon">经度</param>
/// <param name="ALat">纬度</param>
/// <param name="Points">多边形边界点集合</param>
/// <returns></returns>
public static bool IsPtInPoly(double ALon, double ALat, Point[] Points)
{
int iSum, iCount, iIndex;
double dLon1 = 0, dLon2 = 0, dLat1 = 0, dLat2 = 0, dLon;
if (Points.Length < 3)
{
return false;
}
iSum = 0;
iCount = Points.Length;
for (iIndex = 0; iIndex < iCount; iIndex++)
{
if (ALon == Points[iIndex].getX() && ALat == Points[iIndex].getY()) //A点在多边形上
return true;
if (iIndex == iCount - 1)
{
dLon1 = Points[iIndex].getX();
dLat1 = Points[iIndex].getY();
dLon2 = Points[0].getX();
dLat2 = Points[0].getY();
}
else
{
dLon1 = Points[iIndex].getX();
dLat1 = Points[iIndex].getY();
dLon2 = Points[iIndex + 1].getX();
dLat2 = Points[iIndex + 1].getY();
}
//以下语句判断A点是否在边的两端点的纬度之间，在则可能有交点
if (((ALat > dLat1) && (ALat < dLat2)) || ((ALat > dLat2) && (ALat < dLat1)))
{
if (Math.Abs(dLat1 - dLat2) > 0)
{
//获取A点向左射线与边的交点的x坐标：
dLon = dLon1 - ((dLon1 - dLon2) * (dLat1 - ALat)) / (dLat1 - dLat2);
//如果交点在A点左侧，则射线与边的全部交点数加一：
if (dLon < ALon)
{
iSum++;
}
//如果相等，则说明A点在边上
if(dLon==ALon)
return true;
}
}
}
if ((iSum % 2) != 0)
{
return true;
}
return false;
}
}
public class Point
{
private Double x;
private Double y;
public Point(Double x, Double y)
{
this.x = x;
this.y = y;
}
public Double getX()
{
return x;
}
public void setX(Double x)
{
this.x = x;
}
public Double getY()
{
return y;
}
public void setY(Double y)
{
this.y = y;
}
}
}
方法二：Oracle自定义函数法
