__init__ (
        self,
        visible_data,
        xyz_in,
        xyz_out,
        canvas,
        ymin,
        ymax,
        use_volume_color,
        )

calculate_plot_scale ( self )

calculate_value_range ( self,  threshold )

first_maximum_above_threshold ( self )

move_line_cb ( self,  event )

plot_threshold_line (
        self,
        threshold,
        color,
        )

redraw_threshold_line ( self )

trace_values_to_canvas_xy ( self,  tvlist )

volume_color ( self )