How to find the angle between two coordinatess in mapbox

Question

I was working on mapbox and on the basis of my current latlong , a random distance of 226mt and a random degree of 179 degrees , I calculated another latlong as follows.

function findpos(){
    var ptt = new mapboxgl.LngLat(latitude,longitude);
    var ptt2 = destinationPoint(179.85, 0.226, ptt);

    return ptt2;
}


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

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

function destinationPoint(brng, dist, pointA) {
   dist = dist / 6378.1;
   brng = brng.toRad();

   var lat1 = pointA.lat.toRad(), lon1 = pointA.lng.toRad();

   var lat2 = Math.asin(Math.sin(lat1) * Math.cos(dist) +
                        Math.cos(lat1) * Math.sin(dist) * Math.cos(brng));

   var lon2 = lon1 + Math.atan2(Math.sin(brng) * Math.sin(dist) *
                                Math.cos(lat1),
                                Math.cos(dist) - Math.sin(lat1) *
                                Math.sin(lat2));

   if (isNaN(lat2) || isNaN(lon2)) return null;
   console.log("des ",lon2,lat2);
   return new mapboxgl.LngLat(lat2.toDeg(), lon2.toDeg());
}

It was okay till this point.But Now I wanted to find the angle or bearing between two latlongs and found this

// 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;
//  return brng;
}  

It calculates a degree and gives a result. But when i decided to double check this function by putting the already calculated latlongs by the function findpos() above, i should have got the answer as 179.85 degrees , but instead I get the angle as 270 degree .

Which part of the code is correct? I have created a working example here , and have logged the values in the console. Can anyone help me out here please?

Answer 1

You are using the mapboxgl.LngLat() function. The function name already contains the order in which it expects you to pass longitude and latitude -- > first longitude then latitude. You are passing first latitude then longitude. This will definitely cause a problem.

Your code:

 function findpos(){ var ptt = new mapboxgl.LngLat(latitude,longitude); var ptt2 = destinationPoint(179.85, 0.226, ptt); return ptt2; }

Try this:

 function findpos(){ var ptt = new mapboxgl.LngLat(longitude,latitude); var ptt2 = destinationPoint(179.85, 0.226, ptt); return ptt2; }

Similar for this part of your code:

 return new mapboxgl.LngLat(lat2.toDeg(), lon2.toDeg());

Answer 2

Have a look on Turf documentation

It provide's two different methods. You can try:

http://turfjs.org/docs/#bearing

http://turfjs.org/docs/#rhumbBearing