Creights - 1 year ago 104

Javascript Question

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 Source

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