def to_bing_str(self):
        """
        Convert Viewbox object to a string that can be used by Bing
        as a query parameter.
        """
        vb = self.convert_srs(4326)
        return '%s,%s,%s,%s' % (vb.bottom, vb.left, vb.top, vb.right)
Convert Viewbox object to a string that can be used by Bing
        as a query parameter.