def get_last_tid(self):
        try:
            spec = {'tid': {'$gt': 0}}
            sort = [('tid', -1)]
            row = self.db.docs.find_one(spec, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        if row:
            return row['tid']
        return 0
def idq_ld(id, iq, ld, ax=0):
    """creates a surface plot of ld vs. id, iq"""
    if ax == 0:
        _create_3d_axis()
        ax = plt.gca()
    _plot_surface(ax, id, iq, np.asarray(ld)*1e3,
                  (u'Id/A', u'Iq/A', u'L d/mH'),
                  azim=120)