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<form name="distancia">

<input type="text" value = ""   id="lat1">
<input type="text" value = "" id="lon1">
<input type="text" value = "" id="lat2">
<input type="text" value = "" id="lon2">

<input type="button" value = "Calcular" onclick="cal()" name="calcular"/>

</form>


<script type="text/javascript">


function cal(){
    
let lat1 = document.getElementById("lat1");
let lon1 = document.getElementById("lon1");
let lat2 = document.getElementById("lat2");
let lon2 = document.getElementById("lon2");
 alert(getDistanciaMetros(lat1.value,lon1.value,lat2.value,lon2.value));

}


function getDistanciaMetros(lat1,lon1,lat2,lon2)
{

  console.log(" ",lat1," ",lon1," ",lat2," ",lon2);
  rad = function(x) {return x*Math.PI/180;}
  var R = 6378.137; //Radio de la tierra en km 
  var dLat = rad( lat2 - lat1 );
  var dLong = rad( lon2 - lon1 );
  var a = Math.sin(dLat/2) * Math.sin(dLat/2) + Math.cos(rad(lat1)) * 
  Math.cos(rad(lat2)) * Math.sin(dLong/2) * Math.sin(dLong/2);
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));

  //aquí obtienes la distancia en metros por la conversion 1Km =1000m
  var d = (R * c * 1000)/1000; 
  return d ; 
}
</script>