How to use the cjio.geom_help.to_2d function in cjio

total = 0
        for i in range(len(face)):
            total += len(face[i])
            rings[i] = total
        # print(rings)

        # 1. normal with Newell's method
        n, b = geom_help.get_normal_newell(sfv)
        if b == False:
            return (n, False)
        # print ("Newell:", n)
        # 2. project to the plane to get xy
        sfv2d = np.zeros( (sfv.shape[0], 2))
        # print (sfv2d)
        for i,p in enumerate(sfv):
            xy = geom_help.to_2d(p, n)
            # print("xy", xy)
            sfv2d[i][0] = xy[0]
            sfv2d[i][1] = xy[1]
        result = mapbox_earcut.triangulate_float64(sfv2d, rings)
        # print (result.reshape(-1, 3))

        for i,each in enumerate(result):
            # print (sf[i])        
            result[i] = sf[each]
        
        # print (result.reshape(-1, 3))
        return (result.reshape(-1, 3), True)