Annotations on a JFreeChart Pie Chart

Question

Specifically I am looking to add text annotations to specific locations to a JFreeChart that is being output to a png file for web use. Can/how do annotations get added to pie charts. I have been able to successfully add annotations to XYPlots, but don't know how to overlay or add one to a PiePlot.

My full task is to use the PiePlot to create a sort of clock. So far everything has worked great, but now I need to add labels at the 12, 3, 6, and 9 o'clock locations and completely stumped.

Adam

Answer 1

After a fairly strenuous search I don't believe this is currently possible (JFreeChart 1.0.13). Possible options are:

Create a second chart with an XYPlot to generate a second image with needed annotations. Overlay this image on the page. This option is bad because it doubles the number of chart images to be uploaded.

Set the image as a background on the page and HTML the text over the image. Bad because it isn't maintainable and makes a headache of data transfer.

Personally I am just going to find another way to communicate the information in the title, but I wanted to post my findings for the next person. Adam

Answer 2

Bit of an old question, but here's how I did something similar (annotation at 1, 2, 3, ... o'clock positions) using a polar plot. It uses a ChoiceFormatter and the NumberTickUnit:

    final JFreeChart chart = ChartFactory.createPolarChart(
            "HAPI Hourly Usage (UTC)", ds, true, true, false);
    final PolarPlot plot = (PolarPlot) chart.getPlot();

    // Create a ChoiceFormat to map the degrees to clock positions
    double[] limits = new double[12];
    String[] formats = new String[12];
    limits[0] = 0;
    formats[0] = "12";

    // degrees = 360/12
    for (int i = 1; i < limits.length; i++) {
        limits[i] = degrees * (i);
        formats[i] = Integer.toString(i);
    }
    ChoiceFormat clock = new ChoiceFormat(limits, formats);

    TickUnit tickUnit = new NumberTickUnit(degrees, clock);

    // now configure the plot
    plot.setAngleTickUnit(tickUnit); // sets the ticks
    plot.setAngleLabelsVisible(true); // makes the labels visible
    plot.setAngleLabelPaint(Color.LIGHT_GRAY); // user choice
    plot.setAngleGridlinesVisible(true); // must set this to display the
                                         // labels
    plot.setAngleGridlinePaint(Color.BLACK); // plot's background color
                                             // (makes lines invisible)
    plot.setRadiusGridlinesVisible(false); //turn off the radius value circles
    ValueAxis axis = plot.getAxis();
    axis.setTickLabelsVisible(false); //turn off the radius value labels

winds up looking like http://img522.imageshack.us/img522/6693/hapihours.jpg