How to plot color map in java?

Question

I have a dataset with 3 column, x, y, and value at (x,y). I want to plot map similar to bellow map. How to plot this type of figure in jfreechart or any library available for this kind of plot?

Answer 1

Starting with this example and using this idea, you can use a SpectrumPaintScale to get a palette of colors as shown below.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Paint;
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.labels.StandardXYToolTipGenerator;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.PaintScale;
import org.jfree.chart.renderer.xy.XYBlockRenderer;
import org.jfree.chart.title.PaintScaleLegend;
import org.jfree.data.xy.DefaultXYZDataset;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYZDataset;
import org.jfree.chart.ui.RectangleEdge;
import org.jfree.chart.ui.RectangleInsets;

/**
 * @see https://stackoverflow.com/a/37235165/230513
 */
public class XYZChartDemo {

    private static final int N = 100;

    public XYZChartDemo(String title) {
        JFrame f = new JFrame(title);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        ChartPanel chartPanel = new ChartPanel(createChart(createDataset())) {
            @Override
            public Dimension getPreferredSize() {
                return new Dimension(640, 480);
            }
        };
        chartPanel.setMouseZoomable(true, false);
        f.add(chartPanel);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    private static JFreeChart createChart(XYDataset dataset) {
        NumberAxis xAxis = new NumberAxis("x Axis");
        NumberAxis yAxis = new NumberAxis("y Axis");
        XYPlot plot = new XYPlot(dataset, xAxis, yAxis, null);
        XYBlockRenderer r = new XYBlockRenderer();
        r.setDefaultToolTipGenerator(new StandardXYToolTipGenerator());
        SpectrumPaintScale ps = new SpectrumPaintScale(0, N * N);
        r.setPaintScale(ps);
        plot.setRenderer(r);
        JFreeChart chart = new JFreeChart("Title",
            JFreeChart.DEFAULT_TITLE_FONT, plot, false);
        NumberAxis scaleAxis = new NumberAxis("Scale");
        scaleAxis.setAxisLinePaint(Color.white);
        scaleAxis.setTickMarkPaint(Color.white);
        PaintScaleLegend legend = new PaintScaleLegend(ps, scaleAxis);
        legend.setSubdivisionCount(128);
        legend.setAxisLocation(AxisLocation.TOP_OR_RIGHT);
        legend.setPadding(new RectangleInsets(25, 10, 50, 10));
        legend.setStripWidth(20);
        legend.setPosition(RectangleEdge.RIGHT);
        legend.setBackgroundPaint(Color.WHITE);
        chart.addSubtitle(legend);
        chart.setBackgroundPaint(Color.white);
        return chart;
    }

    private static XYZDataset createDataset() {
        DefaultXYZDataset dataset = new DefaultXYZDataset();
        double[][] data = new double[3][N * N];
        for (int i = 0; i < N * N; i++) {
            var x = i % N;
            var y = i / N;
            data[0][i] = x;
            data[1][i] = y;
            data[2][i] = x * y;
        }
        dataset.addSeries("Series", data);
        return dataset;
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            XYZChartDemo demo = new XYZChartDemo("XYZ Demo");
        });
    }

    private static class SpectrumPaintScale implements PaintScale {

        private static final float H1 = 0f;
        private static final float H2 = 1f;
        private final double lowerBound;
        private final double upperBound;

        public SpectrumPaintScale(double lowerBound, double upperBound) {
            this.lowerBound = lowerBound;
            this.upperBound = upperBound;
        }

        @Override
        public double getLowerBound() {
            return lowerBound;
        }

        @Override
        public double getUpperBound() {
            return upperBound;
        }

        @Override
        public Paint getPaint(double value) {
            float scaledValue = (float) (value / (getUpperBound() - getLowerBound()));
            float scaledH = H1 + scaledValue * (H2 - H1);
            return Color.getHSBColor(scaledH, 1f, 1f);
        }
    }
}

Answer 2

An XYBlockRenderer looks like a good match. You can use Color.getHSBColor(), like they show here, to make the PaintScale.

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