Find direction of geographic location relative to heading.

using UnityEngine;

public class GetPointHeading:MonoBehaviour
{
    private OnlineMaps map;
    private float trueHeading;

    private void Start()
    {
        map = OnlineMaps.instance;
 
        OnlineMapsControlBase.instance.OnMapClick += OnMapClick;
        OnlineMapsLocationService.instance.OnCompassChanged += OnCompassChanged;
    }

    private void OnCompassChanged(float f)
    {
        trueHeading = f * 360;
    }

    private void OnMapClick()
    {
        double mx, my, px, py;
        map.GetPosition(out mx, out my);
        OnlineMapsControlBase.instance.GetCoords(out px, out py);

        // Online Maps v2.4 way:
        map.projection.CoordinatesToTile(mx, my, map.zoom, out mx, out my);
        map.projection.CoordinatesToTile(px, py, map.zoom, out px, out py);

        // Online Maps v2.3 way:
        // OnlineMapsUtils.LatLongToTiled(mx, my, map.zoom, out mx, out my);
        // OnlineMapsUtils.LatLongToTiled(px, py, map.zoom, out px, out py);

        // 0 - North, 90 - East, 180 - South, 270 (in this case, the following number is -89) - West
        float heading = (float)OnlineMapsUtils.Angle2D(mx, my, px, py) + 90;

        float relativeHeading = heading - trueHeading;
        if (relativeHeading < -180) relativeHeading += 360;
        else if (relativeHeading > 180) relativeHeading -= 360;

        Debug.Log("Heading: " + heading + ", True Heading: " + trueHeading + ", Relative Heading: " + relativeHeading);
    }
}