function getDistance(lat1, lng1, lat2, lng2){
    
    
  var radLat1 = lat1 * Math.PI / 180.0
  var radLat2 = lat2 * Math.PI / 180.0
  var a = radLat1 - radLat2
  var b = lng1 * Math.PI / 180.0 - lng2 * Math.PI / 180.0
  var s = 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(a / 2), 2) +
  Math.cos(radLat1) * Math.cos(radLat2) * Math.pow(Math.sin(b / 2), 2)))
  s = s * 6378.137// EARTH_RADIUS;
  s = Math.round(s * 10000) / 10000
  if(s<1){
    
    //如果距离小于1km返回m
    s=s.toFixed(3)
    s=s*1000+"m"
  }else{
    
    
    s=s.toFixed(2)
    s=s+"km"
  }
  return s
}