//解平面多边形面积
public double CalPolygon(ShapeFile.Spoint p1, ShapeFile.Spoint p2)
{
double A;//多边形面积
A = p1.x * p2.y - p2.x * p1.y;
return(A / 2);
}
private int L0; //原点经度
//墨卡托投影反算公式
public PointF WGS84ToMecator(ShapeFile.Spoint p)
{
B0 = 0;
L0 = 0;
PointF pf = new PointF();
//注意弧度和度之间的转换
double a = 6378137; //长半轴
double b = 6356752.3142; //短半轴
double e = Math.Sqrt((a * a - b * b) / (a * a)); //第一偏心率
double e2 = (a * a - b * b) / (b * b); //第二偏心率的平方
double K = a * a * Math.Cos(B0 * Math.PI / 180) / b / Math.Sqrt(1 + e2 * Math.Pow(Math.Cos(B0 * Math.PI / 180), 2));
pf.Y = 1; //迭代初值
float temp = 0; //存储pf.Y的上一个值
while (Math.Abs(pf.Y - temp) > Math.Pow(10, -6)) //判断是否收敛
{
temp = pf.Y;
pf.Y = (float)(Math.PI / 2 - 2 * Math.Atan(Math.Exp(-p.y / K) *
Math.Exp(e / 2 * Math.Log((1 - e * Math.Sin(pf.Y)) / (1 + e * Math.Sin(pf.Y))))));//B，弧度值
}
pf.X = (float)(p.x / K + L0);
return(pf);
}
