Calculate angle between two Latitude/Longitude points

Question

Is there a way to calculate angle between two Latitude/Longitude points?

What I am trying to achieve is to know where the user is heading. For example, user is head

Answer 1

function calculateAngle(lat, lng) {
    var checkLengthInterval = 2;

    // Calculate Angle
    //If ObjFeed == [] add first object.
    if (ObjFeed.length == 0) {
        ObjFeed.push({ 'lat': lat, 'lng': lng });
    } else {
        // Get last object from list to calculate angle betwn last and latest.
        var tempNode = ObjFeed[ObjFeed.length - 1];
        // If last lat and lng is same as current it will always return 0 angle.so only push lat lng in obj which is diff than last one.
        if (!(tempNode.lat == lat && tempNode.lng == lng)) {
            ObjFeed.push({ 'lat': lat, 'lng': lng });
        } else {
            console.log('exact match for lat lng');
        }
    }
     // this is for to keep only few objects in the list and remove other
    if (ObjFeed.length >= checkLengthInterval) {
        // calculating angle only if previous data point is available
        ObjFeed = ObjFeed.slice(-1 * checkLengthInterval); // remove all items in array except last two
        var point1 = ObjFeed[ObjFeed.length - checkLengthInterval];
        var point2 = ObjFeed[ObjFeed.length - 1];

        console.log('previous point1', point1);
        console.log('next point2', point2);

        var dLng = (point2.lng - point1.lng);
        var dLat = (point2.lat - point1.lat);

        dLng = dLng * 10000;
        dLat = dLat * 10000;

        var dlat_by_dlan = 0;

        try {
            dlat_by_dlan = dLng / dLat;
        } catch (err) {
            dlat_by_dlan = NaN;
            console.log('Exception: dLat == 0');
        }

        var angleDegreeBearing = 0, angleBearingRad = 0;
        angleBearingRad = Math.atan(dlat_by_dlan);
        angleDegreeBearing = angleBearingRad * 180 / Math.PI;

        if (dLat < 0 && dLng < 0) {
            angleDegreeBearing = angleDegreeBearing + 180;
        } else if (dLat < 0 && dLng > 0) {
            angleDegreeBearing = angleDegreeBearing + 180;
        } else if (dLat == 0 && dLng == 0) {
            angleDegreeBearing = prevVechicleAngle;
        } else if (dlat_by_dlan == NaN) {
            angleDegreeBearing = prevVechicleAngle;
        }

        console.log('angleDegreeBearing', angleDegreeBearing);

    } else {
        // setting up default angle to 0 if previous data point is not available to calculate actual anglle
        console.log('feedArray default angle 0');
        angleDegreeBearing = 0;
    }
    prevVechicleAngle = angleDegreeBearing;
    return angleDegreeBearing;

}