How to position map so two markers are aligned in a vertical line

Question

I am developing an application that uses google map to navigate the user to a given location. I want to orient the map so the destination point always be at the top of the map and the current location marker to be at the bottom and both markers to be vertically aligned and centered in the map (e.g the vertical line between them to be perpendicular to the screen)

My approach is to find the mid point of the markers and than to calculate the bearing to rotate the map so both markers end up vertically aligned and centered. Centering the mid point will center the markers but I can't calculate the correct value for the bearing.

Any help will be appreciated.

EDIT: I've tried Location.bearingTo and Location.distanceBetween. For the same input they return different values and the one returned from Location.distanceBetween is what i am looking for.

EDIT2 (Code example):

public static void positionMap(GoogleMap map, LatLng start, LatLng end) {
    // zoom the map so both locations are visible
    LatLngBounds bounds = LatLngBounds.builder().include(start).include(end).build();
    map.moveCamera(CameraUpdateFactory.newLatLngBounds(bounds, 200));

    // find the bearing
    float[] results = new float[3];
    Location.distanceBetween(
        start.latitude,
        start.longitude,
        end.latitude,
        end.longitude,
        results);
    float bearing = results[2];

    // position the map so the two markers are vertically aligned
    CameraPosition position = map.getCameraPosition();
    CameraPosition cameraPosition = new CameraPosition.Builder(position)
        .target(Utils.median(start, end))
        .bearing(bearing)
        .build();
    map.moveCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
}

Answer 1

Take a look the the distanceBetween method of a location object.

Here is the doc. The initial bearing is the bearing you need to use from the starting point, the final bearing is the bearing you will be on when you reach the destination. I think you would be interested in the initial bearing.

public static void distanceBetween (double startLatitude, double startLongitude, double endLatitude, double endLongitude, float[] results)

Added in API level 1
Computes the approximate distance in meters between two locations, and optionally the initial and final bearings of the shortest path between them. Distance and bearing are defined using the WGS84 ellipsoid.

The computed distance is stored in results[0]. If results has length 2 or greater, the initial bearing is stored in results[1]. If results has length 3 or greater, the final bearing is stored in results[2].

Parameters
startLatitude   the starting latitude
startLongitude  the starting longitude
endLatitude the ending latitude
endLongitude    the ending longitude
results an array of floats to hold the results
Throws
IllegalArgumentException    if results is null or has length < 1

Answer 2

You could try using Location.bearingTo().

Unfortunately this requires converting from LatLng to Location, but that should be simple enough.