def get_point_index(i_point, spacing, origin):
    """
    Convert absolute position of a point into a grid index
    """
    i_pos = tuple([i_point[i] - origin[i] for i in range(len(i_point))])
    i_ind = tuple([int(i_pos[i]/spacing[i]) for i in range(len(i_pos))])
    return i_ind