def draw_axis_labels
      unless @x_axis_label.nil?
        # X Axis
        # Centered vertically and horizontally by setting the
        # height to 1.0 and the width to the width of the graph.
        x_axis_label_y_coordinate = @graph_bottom + LABEL_MARGIN * 2 + @marker_caps_height

        # TODO Center between graph area
        @d.fill = @font_color
        @d.font = @font if @font
        @d.stroke('transparent')
        @d.pointsize = scale_fontsize(@marker_font_size)
        @d.gravity = NorthGravity
        @d = @d.annotate_scaled(@base_image,
                                @raw_columns, 1.0,
                                0.0, x_axis_label_y_coordinate,
                                @x_axis_label, @scale)
        debug { @d.line 0.0, x_axis_label_y_coordinate, @raw_columns, x_axis_label_y_coordinate }
      end

      unless @y_axis_label.nil?
        # Y Axis, rotated vertically
        @d.rotation = -90.0
        @d.gravity = CenterGravity
        @d = @d.annotate_scaled(@base_image,
                                1.0, @raw_rows,
                                @left_margin + @marker_caps_height / 2.0, 0.0,
                                @y_axis_label, @scale)
        @d.rotation = 90.0
      end
    end
def draw_axis_labels
      unless @x_axis_label.nil?
        # X Axis
        # Centered vertically and horizontally by setting the
        # height to 1.0 and the width to the width of the graph.
        x_axis_label_y_coordinate = @graph_bottom + LABEL_MARGIN * 2 + @marker_caps_height

        # TODO Center between graph area
        @d.fill = @font_color
        @d.font = @font if @font
        @d.stroke('transparent')
        @d.pointsize = scale_fontsize(@marker_font_size)
        @d.gravity = NorthGravity
        @d = @d.annotate_scaled(@base_image,
                                @raw_columns, 1.0,
                                0.0, x_axis_label_y_coordinate,
                                @x_axis_label, @scale)
        debug { @d.line 0.0, x_axis_label_y_coordinate, @raw_columns, x_axis_label_y_coordinate }
      end

      unless @y_axis_label.nil?
        # Y Axis, rotated vertically
        @d.rotation = -90.0
        @d.gravity = CenterGravity
        @d = @d.annotate_scaled(@base_image,
                                1.0, @raw_rows,
                                @left_margin + @marker_caps_height / 2.0, 0.0,
                                @y_axis_label, @scale)
        @d.rotation = 90.0
      end
    end
Draw the optional labels for the x axis and y axis.