How to correctly use Crosshair and CrosshairOverlay when there are multiple RangeAxes in JFreeChar

[zfoxbaby]

How to correctly use Crosshair and CrosshairOverlay when there are multiple RangeAxes in JFreeChart? I would like to get your explanation.

As shown in the image, the Crosshair for I1 retrieves the correct value, but its position is incorrect.

SocketDataComposite.java

[zfoxbaby]

I understand now. 🙇‍

@Override
public void chartMouseMoved(ChartMouseEvent event) {
    Rectangle2D dataArea = panel.getScreenDataArea();
    JFreeChart chart = event.getChart();
    XYPlot plot = (XYPlot)chart.getPlot();
    // X
    ValueAxis xAxis = plot.getDomainAxis();
    double x = xAxis.java2DToValue(event.getTrigger().getX(), dataArea, RectangleEdge.BOTTOM);
    xCrosshair.setValue(x);
    // Y
    Map<Integer, XYDataset> datasets = plot.getDatasets();
    Set<Entry<Integer, XYDataset>> entrySet = datasets.entrySet();
    Iterator<Entry<Integer, XYDataset>> iterator = entrySet.iterator();
    Entry<Integer, XYDataset> mainAxisEntry = iterator.next();
    Integer mainIndex = mainAxisEntry.getKey();
    XYDataset mainDataSet = mainAxisEntry.getValue();
    double mainValY = DatasetUtils.findYValue(mainDataSet, 0, x);
    yCrosshairs[mainIndex].setValue(mainValY);
    
    RectangleEdge mainRangeAxisEdge = plot.getRangeAxisEdge(0);
    ValueAxis mainRangeAxis =  plot.getRangeAxis(0);
    while(iterator.hasNext()) {
        Entry<Integer, XYDataset> childRangeAxis = iterator.next();
        XYDataset value = childRangeAxis.getValue();
        Integer key = childRangeAxis.getKey();
        double y = DatasetUtils.findYValue(value, 0, x);
        ValueAxis rangeAxis = plot.getRangeAxis(key);
        double valueToJava = rangeAxis.valueToJava2D(y, dataArea, plot.getRangeAxisEdge(key));
        double transformY = mainRangeAxis.java2DToValue(valueToJava, dataArea, mainRangeAxisEdge);
        yCrosshairs[key].setValue(transformY);
        yCrosshairs[key].setLabelGenerator(ch -> {
            return numberFormat.format(y);
        });
    }
}

[trashgod]

As you have found, java2DToValue() and valueToJava2D() may be used to convert between screen coordinates and the corresponding data value. As the plot already does this to render the crosshair, consider asking the dataset for the desired value, as outlined here and shown here. Related examples may be found here and here.