public double distance(double n1, double e1, double n2, double e2)  
     {  
         double jl_jd = 102834.74258026089786013677476285//每经度单位米;  
         double jl_wd = 111712.69150641055729984301412873//每纬度单位米;  
         double b = Math.abs((e1 - e2) * jl_jd);  
         double a = Math.abs((n1 - n2) * jl_wd);  
         return Math.sqrt((a * a + b * b));  
  
     }