ChartDirector Ver 3.0 (Python Edition)

Y-Axis Scaling


        

This example illustrates how to control scaling of an axis.

By default, ChartDirector will auto-scaled 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 three charts demonstrates the effects of different top/bottom extensions. (Please refer to Axis.setAutoScale on what these parameters mean.)

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

The fifth chart demonstrates using manual scaling instead of auto-scaling. A manual linear scale can be configured using Axis.setLinearScale or Axis.setLinearScale2. ChartDirector also supports Axis.setLogScale, Axis.setLogScale2, Axis.setDateScale and Axis.setDateScale2 for configuring manual log and date scales.

Source Code Listing

[File: pythondemo/axisscale.py] (The CGI version is available as "pythondemo_cgi/axisscale.py".)
#!/usr/bin/python from pychartdir import * def createChart(img) : #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 180 pixels c = XYChart(200, 180) #Set the plot area at (30, 20) and of size 140 x 130 pixels c.setPlotArea(30, 20, 140, 130) #Configure the axis as according to the input parameter if img == "0" : c.addTitle("No Axis Extension", "arial.ttf", 8) elif img == "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) elif img == "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) elif img == "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) #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" % img) createChart("0") createChart("1") createChart("2") createChart("3") createChart("4")