#pragma mark - calculate distance  根据2个经纬度计算距离

 #define PI 3.14159265358979323

 +(double) CalculationDistanceOther_Lon1:(double)lon1 Other_Lat1:(double)lat1 self_Lon2:(double)lon2 self_Lat2:(double)lat2{

     double er = ; // 6378700.0f;

     //ave. radius = 6371.315 (someone said more accurate is 6366.707)

     //equatorial radius = 6378.388

     //nautical mile = 1.15078

     double radlat1 = PI*lat1/180.0f;

     double radlat2 = PI*lat2/180.0f;

     //now long.

     double radlong1 = PI*lon1/180.0f;

     double radlong2 = PI*lon2/180.0f;

     if( radlat1 <  ) radlat1 = PI/ + fabs(radlat1);// south

     if( radlat1 >  ) radlat1 = PI/ - fabs(radlat1);// north

     if( radlong1 <  ) radlong1 = PI* - fabs(radlong1);//west

     if( radlat2 <  ) radlat2 = PI/ + fabs(radlat2);// south

     if( radlat2 >  ) radlat2 = PI/ - fabs(radlat2);// north

     if( radlong2 <  ) radlong2 = PI* - fabs(radlong2);// west

     //spherical coordinates x=r*cos(ag)sin(at), y=r*sin(ag)*sin(at), z=r*cos(at)

     //zero ag is up so reverse lat

     double x1 = er * cos(radlong1) * sin(radlat1);

     double y1 = er * sin(radlong1) * sin(radlat1);

     double z1 = er * cos(radlat1);

     double x2 = er * cos(radlong2) * sin(radlat2);

     double y2 = er * sin(radlong2) * sin(radlat2);

     double z2 = er * cos(radlat2);

     double d = sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)+(z1-z2)*(z1-z2));

     //side, side, side, law of cosines and arccos

     double theta = acos((er*er+er*er-d*d)/(*er*er));

     double dist  = theta*er;

     return dist;

 }