Y-Axis Scaling

This example demonstrates how to control auto-scaling.

By default, ChartDirector auto-scales all axes. The Axis.setAutoScale method controls the top extension, bottom extension and the zero affinity parameters that ChartDirector uses during auto-scaling. The first two parameters determine the amount of top and bottom margins to reserve during auto-scaling, while the last parameter determines when the axis should start from the origin (0).

The first 3 charts demonstrate the effects of different top/bottom extensions.

The 4th chart demonstrates that one could exclude a segment on the ends of an axis from scaling using Axis.setMargin.

The 5th chart demonstrates manual scaling instead of auto-scaling. In manual scaling, the axis scale is explicitly provided by using Axis.setLinearScale, Axis.setLinearScale2, Axis.setLogScale, Axis.setLogScale2, Axis.setDateScale or Axis.setDateScale2.

[Ruby On Rails Version - Controller] app/controllers/axisscale_controller.rb

require("chartdirector")

class AxisscaleController < ApplicationController

    def index()
        @title = "Y-Axis Scaling"
        @ctrl_file = File.expand_path(__FILE__)
        @noOfCharts = 5
        render :template => "templates/chartview"
    end

    #
    # Render and deliver the chart
    #
    def getchart()
        # This script can draw different charts depending on the chartIndex
        chartIndex = (params["img"]).to_i

        # The data for the chart
        data = [5.5, 3.5, -3.7, 1.7, -1.4, 3.3]
        labels = ["Jan", "Feb", "Mar", "Apr", "May", "Jun"]

        # Create a XYChart object of size 200 x 190 pixels
        c = ChartDirector::XYChart.new(200, 190)

        # Set the plot area at (30, 20) and of size 140 x 140 pixels
        c.setPlotArea(30, 20, 140, 140)

        # Configure the axis as according to the input parameter
        if chartIndex == 0
            c.addTitle("No Axis Extension", "arial.ttf", 8)
        elsif chartIndex == 1
            c.addTitle("Top/Bottom Extensions = 0/0", "arial.ttf", 8)
            # Reserve 20% margin at top of plot area when auto-scaling
            c.yAxis().setAutoScale(0, 0)
        elsif chartIndex == 2
            c.addTitle("Top/Bottom Extensions = 0.2/0.2", "arial.ttf", 8)
            # Reserve 20% margin at top and bottom of plot area when auto-scaling
            c.yAxis().setAutoScale(0.2, 0.2)
        elsif chartIndex == 3
            c.addTitle("Axis Top Margin = 15", "arial.ttf", 8)
            # Reserve 15 pixels at top of plot area
            c.yAxis().setMargin(15)
        else
            c.addTitle("Manual Scale -5 to 10", "arial.ttf", 8)
            # Set the y axis to scale from -5 to 10, with ticks every 5 units
            c.yAxis().setLinearScale(-5, 10, 5)
        end

        # Set the labels on the x axis
        c.xAxis().setLabels(labels)

        # Add a color bar layer using the given data. Use a 1 pixel 3D border for the bars.
        c.addBarLayer3(data).setBorderColor(-1, 1)

        # Output the chart
        send_data(c.makeChart2(ChartDirector::PNG), :type => "image/png", :disposition => "inline")

    end

end

[Ruby On Rails Version - View] app/views/templates/chartview.html.erb

<html>
<body style="margin:5px 0px 0px 5px">

<!-- Title -->
<div style="font-size:18pt; font-family:verdana; font-weight:bold">
    <%= @title %>
</div>
<hr style="border:solid 1px #000080" />

<!-- Source Code Listing Link -->
<div style="font-size:9pt; font-family:verdana; margin-bottom:1.5em">
    <%= link_to "Source Code Listing", 
        :controller => "cddemo", :action => "viewsource",
        :ctrl_file => @ctrl_file, :view_file => File.expand_path(__FILE__) %>
</div>

<!-- Create one or more IMG tags to display the demo chart(s) -->
<% 0.upto(@noOfCharts - 1) do |i| %>
    <img src="<%= url_for(:action => "getchart", :img => i) %>">
<% end %>

</body>
</html>

[Command Line Version] rubydemo/axisscale.rb

#!/usr/bin/env ruby
require("chartdirector")

def createChart(chartIndex)

    # The data for the chart
    data = [5.5, 3.5, -3.7, 1.7, -1.4, 3.3]
    labels = ["Jan", "Feb", "Mar", "Apr", "May", "Jun"]

    # Create a XYChart object of size 200 x 190 pixels
    c = ChartDirector::XYChart.new(200, 190)

    # Set the plot area at (30, 20) and of size 140 x 140 pixels
    c.setPlotArea(30, 20, 140, 140)

    # Configure the axis as according to the input parameter
    if chartIndex == 0
        c.addTitle("No Axis Extension", "arial.ttf", 8)
    elsif chartIndex == 1
        c.addTitle("Top/Bottom Extensions = 0/0", "arial.ttf", 8)
        # Reserve 20% margin at top of plot area when auto-scaling
        c.yAxis().setAutoScale(0, 0)
    elsif chartIndex == 2
        c.addTitle("Top/Bottom Extensions = 0.2/0.2", "arial.ttf", 8)
        # Reserve 20% margin at top and bottom of plot area when auto-scaling
        c.yAxis().setAutoScale(0.2, 0.2)
    elsif chartIndex == 3
        c.addTitle("Axis Top Margin = 15", "arial.ttf", 8)
        # Reserve 15 pixels at top of plot area
        c.yAxis().setMargin(15)
    else
        c.addTitle("Manual Scale -5 to 10", "arial.ttf", 8)
        # Set the y axis to scale from -5 to 10, with ticks every 5 units
        c.yAxis().setLinearScale(-5, 10, 5)
    end

    # Set the labels on the x axis
    c.xAxis().setLabels(labels)

    # Add a color bar layer using the given data. Use a 1 pixel 3D border for the bars.
    c.addBarLayer3(data).setBorderColor(-1, 1)

    # Output the chart
    c.makeChart("axisscale%s.png" % chartIndex)
end

createChart(0)
createChart(1)
createChart(2)
createChart(3)
createChart(4)