Multiple axes on the same data

Question

I'm trying to have two axes on the same data.

The data is a couple of DefaultTableXYDatasets. The plot is a XYPlot, and I have two XYLineAndShapeRenderers and one StackedXYAreaRenderer2.

All data is in meters for the y-values, and I want to have one axis displaying it in meters and one axis displaying it in feet. Now this feels like a common thing to do, but I can't decide on the most obvious way to do it. One way that works would be to duplicate the data and have the y-values in feet, then add another NumberAxis and be done with it.

But I thought it would be wiser to subclass NumberAxis, or inject some functionality into NumberAxis to scale the values. Or should I go with the first approach?

What do you think?

Predestinate

Replace the natural language with programming language in your question. A much better way to start a conversation on SO :) – Openmouthed

The demo has lots of multiple axis examples. – Twoup

Yes, but I haven't seen any example where there's more than one axis to one dataset. I might be mistaken, I'll check them again – Predestinate

Answer 1

Eventually i settled on this solution, it might not be the most elegant but it worked. I have a second axis feetAxis, and added a AxisChangeListener on the first axis called meterAxis. When the meterAxis changes set the range on feetAxis.

I used SwingUtilities.invokeLater, otherwise the range would be incorrect when zooming out of the chart, then the feetAxis would only go from 0 to 1. Didn't check why though.

feetAxis = new NumberAxis("Height [ft]");
metersAxis = new NumberAxis("Height [m]");
pathPlot.setRangeAxis(0, metersAxis);
pathPlot.setRangeAxis(1, feetAxis);

metersAxis.addChangeListener(new AxisChangeListener() {

   @Override
   public void axisChanged(AxisChangeEvent event) {

       SwingUtilities.invokeLater(new Runnable() {

           @Override
           public void run() {
               feetAxis.setRange(metersAxis.getLowerBound() * MetersToFeet, metersAxis.getUpperBound() * MetersToFeet);
                }
           });
       }
   });

Predestinate

Answer 2

To avoid duplicating data, you can use the XYPlot method mapDatasetToRangeAxes() to map a dataset index to a list of axis indices. In the example below, meters is the principle axis, and the range of the corresponding feet axis is scaled accordingly, as shown here. Note that invokeLater() is required to ensure that the feet axis is scaled after any change in the meters axis.

import java.awt.EventQueue;
import java.util.Arrays;
import java.util.List;
import javax.swing.JFrame;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.axis.AxisLocation;
import org.jfree.chart.axis.NumberAxis;
import org.jfree.chart.axis.ValueAxis;
import org.jfree.chart.event.AxisChangeEvent;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.XYItemRenderer;
import org.jfree.chart.renderer.xy.XYLineAndShapeRenderer;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;

/**
 * @see https://mcmap.net/q/426299/-multiple-axes-on-the-same-data/230513
 */
public class AxisTest {

    private static final int N = 5;
    private static final double FEET_PER_METER = 3.28084;

    private static XYDataset createDataset() {
        XYSeriesCollection data = new XYSeriesCollection();
        final XYSeries series = new XYSeries("Data");
        for (int i = -N; i < N * N; i++) {
            series.add(i, i);
        }
        data.addSeries(series);
        return data;
    }

    private JFreeChart createChart(XYDataset dataset) {
        NumberAxis meters = new NumberAxis("Meters");
        NumberAxis feet = new NumberAxis("Feet");
        ValueAxis domain = new NumberAxis();
        XYItemRenderer renderer = new XYLineAndShapeRenderer();
        XYPlot plot = new XYPlot(dataset, domain, meters, renderer);
        plot.setRangeAxis(1, feet);
        plot.setRangeAxisLocation(1, AxisLocation.BOTTOM_OR_LEFT);
        List<Integer> axes = Arrays.asList(0, 1);
        plot.mapDatasetToRangeAxes(0, axes);
        scaleRange(feet, meters);
        meters.addChangeListener((AxisChangeEvent event) -> {
            EventQueue.invokeLater(() -> {
                scaleRange(feet, meters);
            });
        });
        JFreeChart chart = new JFreeChart("Axis Test",
            JFreeChart.DEFAULT_TITLE_FONT, plot, true);
        return chart;
    }

    private void scaleRange(NumberAxis feet, NumberAxis meters) {
        feet.setRange(meters.getLowerBound() * FEET_PER_METER,
            meters.getUpperBound() * FEET_PER_METER);
    }

    private void display() {
        JFrame f = new JFrame("AxisTest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new ChartPanel(createChart(createDataset())));
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            new AxisTest().display();
        });
    }
}

Alternatively, you can use a JCheckBox to flip between the two series, meters & feet, as shown in this related example. Using the methods available to XYLineAndShapeRenderer, you can hide a second series' lines, shapes and legend. The series itself must be visible to establish the axis range.

Levileviable