JFreechart draw arc on chart

问题

I have 2 questions

1)I am trying to draw an arc on an XYplot using the shape annotation. I used the XYLine annotation to draw a line and I want the arc to start where the line ends. I am having some issues with the parameters.I want the arc to have a height of 17, width 44, and start at the point(3.0, 17) of the plot(this is where the line ends). But the code below does not work. Can someone please tell me what is wrong with the code?

Arc2D.Double arc = new Arc2D.Double(3.0, 
                        16.9,
                        44.0,
                        17.04, 
                        180.0,
                        180.0,
                        Arc2D.OPEN 
                );
plot.addAnnotation(new XYShapeAnnotation(arc,
                        new BasicStroke(2.0f), Color.white));
XYLineAnnotation a1 = new XYLineAnnotation(3.0, 0.0, 3.0,
                        16.9, new BasicStroke(2.0f), Color.white);

2)How can I draw a similar figure on a polar plot?

Thanks

回答1:

1. The critical thing about Arc2D is the bounding rectangle. To make the half-arc H units high, the bounds must be 2 * H units high.

2. AFAIK, PolarPlot does not support annotations.

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.geom.Arc2D;
import java.util.Random;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartFrame;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.annotations.XYLineAnnotation;
import org.jfree.chart.annotations.XYShapeAnnotation;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.chart.plot.XYPlot;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;

/** @see http://stackoverflow.com/questions/6604211 */
public class ArcTest {

    private static final Random r = new Random();
    private static final double PI = 180d;
    private static final int X = 3;
    private static final int Y = 0;
    private static final int W = 44;
    private static final int H = 17;

    public static void main(String[] args) {
        JFreeChart chart = ChartFactory.createXYLineChart(
            "ArcTest", "X", "Y", createDataset(),
            PlotOrientation.VERTICAL, true, true, false);
        XYPlot plot = chart.getXYPlot();
        XYLineAnnotation line = new XYLineAnnotation(
            X, Y, X, H, new BasicStroke(2f), Color.blue);
        plot.addAnnotation(line);
        Arc2D.Double arc = new Arc2D.Double(
            X, Y, W, 2 * H, PI, PI, Arc2D.OPEN);
        plot.addAnnotation(new XYShapeAnnotation(arc,
            new BasicStroke(2.0f), Color.blue));
        ChartFrame frame = new ChartFrame("First", chart);
        frame.pack();
        frame.setVisible(true);
    }

    private static XYDataset createDataset() {
        XYSeriesCollection result = new XYSeriesCollection();
        XYSeries series = new XYSeries("ArcTest");
        series.add(0, 0);
        series.add(W, W);
        result.addSeries(series);
        return result;
    }
}

来源：https://stackoverflow.com/questions/6604211/jfreechart-draw-arc-on-chart