def __call__(self):
        vmin, vmax = self.axis.get_view_interval()
        ticks = self.tick_values(vmin, vmax)
        # Make sure that first and last tick are the start
        # and the end of the genomic range plotted. If next
        # ticks are too close, remove them.
        ticks[0] = vmin
        ticks[-1] = vmax
        if ticks[1] - vmin < (vmax - vmin)/(self._nbins*3):
            ticks = np.delete(ticks, 1)
        if vmax - ticks[-2] < (vmax - vmin)/(self._nbins*3):
            ticks = np.delete(ticks, -2)
        return self.raise_if_exceeds(np.array(ticks))