经纬度转换为距离单位（m,km）的方法

求百度地图中把经纬度转换为距离单位（m,km）的稳妥方法

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如果是直线距离的话 那么只要有比例尺 画个坐标轴 似乎就可以计算了

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function getDistanceFromLatLonInKm(lat1,lon1,lat2,lon2) {
  var R = 6371; // Radius of the earth in km
  var dLat = deg2rad(lat2-lat1);  // deg2rad below
  var dLon = deg2rad(lon2-lon1); 
  var a = 
    Math.sin(dLat/2) * Math.sin(dLat/2) +
    Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) * 
    Math.sin(dLon/2) * Math.sin(dLon/2)
    ; 
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
  var d = R * c; // Distance in km
  return d;
}

function deg2rad(deg) {
  return deg * (Math.PI/180)
}

参考

• http://stackoverflow.com/questions/27928/calculate-distance-between-two-latitude-longitude-points-haversine-formula?page=1&tab=votes#tab-top

• https://en.wikipedia.org/wiki/Haversine_formula