/**** 根据两站点的经纬度求两站点间的距离 ****/
double D_jw(double wd1,double jd1,double wd2,double jd2)
{
double x,y,out;
double PI=3.14159265;
double R=6.371229*1e6;
x=(jd2-jd1)*PI*R*cos( ((wd1+wd2)/2) *PI/180)/180;
y=(wd2-wd1)*PI*R/180;
out=hypot(x,y);
return out/1000;
}