'nth_coord = along which coordinate value varies
in 2d, nth_coord = 0 ->  x axis, nth_coord = 1 -> y axis'

def __init__(self, axes, loc, nth_coord=None):

    super(AxisArtistHelperRectlinear.Fixed, self).__init__(loc, nth_coord)
    self.axis = [axes.xaxis, axes.yaxis][self.nth_coord]
