Creights Creights - 4 months ago 37
Javascript Question

Using the Haversine Formula in Javascript

I'm trying to use the Haversine Distance Formula (as found here: http://www.movable-type.co.uk/scripts/latlong.html) but I can't get it to work, please see the following code

function test() {
var lat2 = 42.741;
var lon2 = -71.3161;
var lat1 = 42.806911;
var lon1 = -71.290611;

var R = 6371; // km
//has a problem with the .toRad() method below.
var dLat = (lat2-lat1).toRad();
var dLon = (lon2-lon1).toRad();
var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
Math.cos(lat1.toRad()) * Math.cos(lat2.toRad()) *
Math.sin(dLon/2) * Math.sin(dLon/2);
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
var d = R * c;

alert(d);
}


And the error is:

Uncaught TypeError: Object -0.06591099999999983 has no method 'toRad'


Which I understand to be because it needs to do the following:

Number.prototype.toRad = function() {
return this * Math.PI / 180;
}


But when I put this below the function, it still comes back with the same error message. How do I make it use the helper method? Or is there an alternative way to code this to get it to work? Thanks!

Answer

This code is working:

Number.prototype.toRad = function() {
   return this * Math.PI / 180;
}

var lat2 = 42.741; 
var lon2 = -71.3161; 
var lat1 = 42.806911; 
var lon1 = -71.290611; 

var R = 6371; // km 
//has a problem with the .toRad() method below.
var x1 = lat2-lat1;
var dLat = x1.toRad();  
var x2 = lon2-lon1;
var dLon = x2.toRad();  
var a = Math.sin(dLat/2) * Math.sin(dLat/2) + 
                Math.cos(lat1.toRad()) * Math.cos(lat2.toRad()) * 
                Math.sin(dLon/2) * Math.sin(dLon/2);  
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
var d = R * c; 

alert(d);

Notice how I defined x1 and x2. Play with it at: https://tinker.io/3f794