Draw circle on earth

Circle.java

    GeometryLayer geomLayer = new GeometryLayer(proj);
    // circle of 1000 km around London
    addCircle(geomLayer, new MapPos(0,51), 1000);
    mapView.getLayers().addLayer(geomLayer);

    /**
     * Draw circle around given point, from latitude/longitude
     * Note: many parameters are hardcoded, like style, circle resolution etc - feel free to modify or make parametric
     * @param gl GeometryLayer where circle is added
     * @param circlePos Location of circle center, in longitude (x) and latitude (y)
     * @param radius circle radius in kilometers
     */
    private void addCircle(GeometryLayer gl, MapPos circlePos, double radius){

        // constants
        double earthRadius = 6371000; // in m

        // input
        radius *= 1000; // from km to m
        
        double cLon = circlePos.x * Const.DEG_TO_RAD;
        double cLat = circlePos.y * Const.DEG_TO_RAD;
        double d = radius / earthRadius;
        
        PolygonStyle polyStyle = PolygonStyle.builder()
                .setColor(Color.GREEN & 0x20ffffff)
                .setLineStyle(LineStyle.builder().setColor(Color.BLACK).build())
                .build();
        List<MapPos> mp = new ArrayList<MapPos>();

        for(int i=0; i<360; i+=20){
            double bearing = i * Math.PI / 180;
            double lat = Math.asin(Math.sin(cLat) * Math.cos(d) + Math.cos(cLat) * Math.sin(d) * Math.cos(bearing));
            double lon = (cLon + Math.atan2(Math.sin(bearing) * Math.sin(d) * Math.cos(cLat), Math.cos(d) - Math.sin(cLat) * Math.sin(lat))) * Const.RAD_TO_DEG;
            lat *= Const.RAD_TO_DEG;
            MapPos mapPos = new MapPos(gl.getProjection().fromWgs84(lon, lat));
            mp.add(mapPos);
        }
        
        Polygon poly = new Polygon(mp, null, polyStyle, null);
        gl.add(poly);
    }