show slope of waypoints

def wp_slope(self):
        '''show slope of waypoints'''
        last_w = None
        for i in range(1, self.wploader.count()):
            w = self.wploader.wp(i)
            if w.command not in [mavutil.mavlink.MAV_CMD_NAV_WAYPOINT, mavutil.mavlink.MAV_CMD_NAV_LAND]:
                continue
            if last_w is not None:
                if last_w.frame != w.frame:
                    print("WARNING: frame change %u -> %u at %u" % (last_w.frame, w.frame, i))
                delta_alt = last_w.z - w.z
                if delta_alt == 0:
                    slope = "Level"
                else:
                    delta_xy = mp_util.gps_distance(w.x, w.y, last_w.x, last_w.y)
                    slope = "%.1f" % (delta_xy / delta_alt)
                print("WP%u: slope %s" % (i, slope))
            last_w = w