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 you require an accurate method on an ellipsoid of revolution (i.e. WGS 84), the algorithms get really heavy. You may benefit from GeographicLib, which has been implemented in C/C++, Java, JavaScript, Python, Matlab/Octave, and others.

For the question, there is either a geodesic or a rhumb line between the first and second point.

Geodesic

A geodesic is the shortest path between two points on a curved surface. It is the most common interpretation of where a "user is heading" (from the question), since it is the shortest and most direct. An inverse geodesic calculation can be solved using GeodSolve. You can also use the online interface. This tool has the input/output:

lat1 lon1 lat2 lon2 → azi1 azi2 s12

Where lat1 lon1 is the coordinate pair for the first point, and lat2 lon2 is the coordinate pair for the second point. All units are in degrees (not radians). The result, azi1 or α₁, is the azimuth (a.k.a. bearing) from the start point, given in degrees clockwise from north. The second azimuth is at the second point, because the angle between the two points along a geodesic is not constant. And s12 is the distance between the two points, in metres, with an accuracy of 15 nm.

Rhumb line

A rhumb line connects two coordinate points with a constant azimuth (or bearing). An inverse rhumb line calculation can be solved using RhumbSolve. You can also use the online interface. This tool has the input/output:

lat1 lon1 lat2 lon2 → azi12 s12

These parameters are the same as GeodSolve, except that azi12 is a constant angle between the points.