def remove_small_boxes(proposal, min_size):
    """
    Arguments:
        proposal (tensor): (N, 5)  xc,yc,w,h,theta
        min_size (int)
    """
    _, _, ws, hs, _ = proposal.unbind(dim=1)
    keep = (
        (ws >= min_size) & (hs >= min_size)
    ).nonzero().squeeze(1)
    return keep