获取ARCore的水平方向的FOV

frame = session.update();
if(frame != null && fov == 0){
    Camera camera = frame.getCamera();
    if(camera != null){
        float[] projmtx = new float[16];
        camera.getProjectionMatrix(projmtx, 0, 0.1f, 100.0f);
        fov = (float) (2.0 * Math.atan(1.0 / projmtx[5]) * 180.0 / Math.PI);
    }
}