Calculate bearing between 2 points with javascript

Question

I want to calculate the bearing from point 1 to point 2 The input format is 52.070564 - 4.407116

No matter what i try i cannot get an correct output.

The formula i use is :

// koers berekenen
var y = Math.sin(ln-ln1) * Math.cos(lt);
var x = Math.cos(lt1)*Math.sin(lt) -
        Math.sin(lt1)*Math.cos(lt)*Math.cos(ln-ln1);
var radians = Math.atan2(y, x);
var bearing = Math.round(radians * (180/Math.PI));

/* >>>>>> original <<<<<<<
var y = Math.sin(λ2-λ1) * Math.cos(φ2);
var x = Math.cos(φ1)*Math.sin(φ2) -
        Math.sin(φ1)*Math.cos(φ2)*Math.cos(λ2-λ1);
var brng = Math.atan2(y, x).toDegrees();

φ1,λ1 is the start point, φ2,λ2 the end point (Δλ is the difference in longitude)
*/

Walk

Can you give us some example inputs and example outputs? – Monkshood

Math.sin() and Math.cos() expect their inputs to be in radians. It looks like your inputs are degrees, so you need to convert them. – Itchy

@Walk check my solution – Galiot

52.07129-4.4056 and 52.07091-4.4048 should give a bearing around 230* – Walk

Your snippet produces: "message": "Uncaught ReferenceError: ln is not defined", "filename": "stacksnippets.net/js", – Aorta

Answer 1

You can calculate bearing using this functions:

// Converts from degrees to radians.
function toRadians(degrees) {
  return degrees * Math.PI / 180;
};
 
// Converts from radians to degrees.
function toDegrees(radians) {
  return radians * 180 / Math.PI;
}


function bearing(startLat, startLng, destLat, destLng){
  startLat = toRadians(startLat);
  startLng = toRadians(startLng);
  destLat = toRadians(destLat);
  destLng = toRadians(destLng);

  y = Math.sin(destLng - startLng) * Math.cos(destLat);
  x = Math.cos(startLat) * Math.sin(destLat) -
        Math.sin(startLat) * Math.cos(destLat) * Math.cos(destLng - startLng);
  brng = Math.atan2(y, x);
  brng = toDegrees(brng);
  return (brng + 360) % 360;
}

Cassandry

Answer 2

start_latitude  = 12.9389352
start_longitude = 77.6994306
stop_latitude   = 12.939103
stop_longitude  = 77.705825

var y = Math.sin(stop_longitude-start_longitude) * Math.cos(stop_latitude);
var x = Math.cos(start_latitude)*Math.sin(stop_latitude) -
        Math.sin(start_latitude)*Math.cos(stop_latitude)*Math.cos(stop_longitude-start_longitude);
var brng = Math.atan2(y, x) * 180 / Math.PI;


alert("Bearing in degreee:  " + brng);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

Galiot

Clear, so my input needs to be in radians? I will try to find how to convert this. Thanks! – Walk

I tried but still not the expected result. I change the input from degrees to radius with (* Math.PI / 180). When i take 2 points, one is my garden and the other is on the other side of the street i get a bearing of 20. But when i get the compass on my iphone the bearing to that point is 250. Am i making a mistake in thinking??? – Walk

works great for me using leaflet maps with and real-time moving objects. ive created a compass out of the result using css transforms. – Shit