def __init__(self, aux_trans,
                 extreme_finder=None,
                 grid_locator1=None,
                 grid_locator2=None,
                 tick_formatter1=None,
                 tick_formatter2=None):
        """
        aux_trans : a transform from the source (curved) coordinate to
        target (rectlinear) coordinate. An instance of MPL's Transform
        (inverse transform should be defined) or a tuple of two callable
        objects which defines the transform and its inverse. The callables
        need take two arguments of array of source coordinates and
        should return two target coordinates:
          e.g. x2, y2 = trans(x1, y1)
        """
        super(GridHelperCurveLinear, self).__init__()

        self.grid_info = None
        self._old_values = None
        #self._grid_params = dict()

        self.grid_finder = GridFinder(aux_trans,
                                      extreme_finder,
                                      grid_locator1,
                                      grid_locator2,
                                      tick_formatter1,
                                      tick_formatter2)