Prevent JFreeChart DialPlot wrapping around with large values?

Question

My data value can vary between 0-100. I would like to display a JFreeChart DialPlot showing the range 0-30, where values larger than 30 are displayed by having the needle fi

Answer 1

I've just figured out a work-around answer, but I would be interested to hear if there are better methods.

In this solution, I maintain two DefaultValueDataset objects. One contains the real value and one contains a constrained value, no larger than my dial limit. The needle is associated with the constrained set and the dial value is linked to the real value.

public class DemoChartProblem {

  private static final int DISPLAY_MAX = 30;
  private final DefaultValueDataset dataset = new DefaultValueDataset();
  private final DefaultValueDataset displayDataset = new DefaultValueDataset();
  private final JFrame frame = new JFrame();

  public static void main(String[] args) throws Exception {
    new DemoChartProblem();
  }

  public DemoChartProblem() {
    frame.setPreferredSize(new Dimension(300, 300));
    frame.add(buildDialPlot(0, DISPLAY_MAX, 5));
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

    setValue(50);

    SwingUtilities.invokeLater(new Runnable() {
      @Override
      public void run() {
        frame.setVisible(true);
      }
    });
  }

  private void setValue(int value) {
    dataset.setValue(value);
    displayDataset.setValue(Math.min(DISPLAY_MAX, value));
  }

  private ChartPanel buildDialPlot(int minimumValue, int maximumValue,
      int majorTickGap) {

    DialPlot plot = new DialPlot();
    plot.setDataset(0, dataset);
    plot.setDataset(1, displayDataset);

    plot.setDialFrame(new StandardDialFrame());

    // value indicator uses the real data set
    plot.addLayer(new DialValueIndicator(0));

    // needle uses constrained data set
    plot.addLayer(new DialPointer.Pointer(1));

    StandardDialScale scale = new StandardDialScale(minimumValue, maximumValue,
        -120, -300, majorTickGap, majorTickGap - 1);
    scale.setTickRadius(0.88);
    scale.setTickLabelOffset(0.20);
    plot.addScale(0, scale);

    return new ChartPanel(new JFreeChart(plot));
  }
}

Answer 2

I would be interested to hear if there are better methods.

The disparity between the DialValueIndicator and the maximumValue may be confusing. As an alternative, signify distinct ranges using StandardDialRange:

int redLine = 3 * maximumValue / 5;
plot.addLayer(new StandardDialRange(minimumValue, redLine, Color.blue));
plot.addLayer(new StandardDialRange(redLine, maximumValue, Color.red));

Setting the frame's preferred size is problematic. Instead, override the getPreferredSize() method of ChartPanel:

return new ChartPanel(new JFreeChart(plot)) {
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(300, 300);
    }
};