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

If your are using google maps(Android), there is an easy way - Use SphericalUtil

double angle = SphericalUtil.computeHeading(fromLatLng, toLatLng);

Consider we have 2 points and its lat and lng Then create its Latlng object

LatLng latlng = new LatLng(latValue, lngValue);

After getting Latlng of 2 points, use sperical util to get angle

//import com.google.maps.android.SphericalUtil;
double sphericalValue = SphericalUtil.computeHeading(latLng1, latLng2);

SpericalValue is the angle. Consider you have a car icon and turn it accordingly to the direction its going. Here its from latLng1 to latLng2 then

Bitmap vehiclePin = rotateIconBitmap(sphericalValue);
mMap.addMarker(new MarkerOptions().anchor(0.5f, 0.5f).position(latLng2))
               .setIcon(BitmapDescriptorFactory.fromBitmap(vehiclePin));

use the method below to rotate

    Bitmap rotateIconBitmap(double angle) {
       Bitmap source = BitmapFactory.decodeResource(getResources(), 
                                          R.drawable.ic_vehicle_say_car);
       Matrix matrix = new Matrix();
       matrix.postRotate((float) angle);
       return Bitmap.createBitmap(source, 0, 0, 
                    source.getWidth(), source.getHeight(), matrix, true);
    }

Easy way to achieve uber like rotated icons

Note:- You may have to add an offset of say 90 degree if the marker icon is not pointed to zero degree

The android sphericalutil is open source, refer it if you are using java, you can make use of it.

https://github.com/googlemaps/android-maps-utils/blob/master/library/src/com/google/maps/android/SphericalUtil.java