JMSL Chart Guide: Heatmap

JMSL Chart Programmer's Guide

Heatmap

A heatmap divides a rectangle into subrectangles. The color of each subrectangle is determined by the value of a data array and a colormap.

If the data array is m by n then there are m divisions along the x-axis and n divisions along the y-axis.

A colormap is a mapping from [0,1] to color values. The blue-red colormap, used in the example below, maps 0 to red and 1 to dark blue and interpolates between these endpoints values. The heatmap maps the minimum data value to the color corresponding to 0 and the highest data value to the color corresponding to 1.

The Heatmap class has a special legend for colormaps. It displays the color values as a gradient labeled with corresponding data values.

Example

In this example a two-dimensional array of data is plotted as a heatmap. The "red- blue" colormap is used. The heatmap legend is enabled by settings its "Paint" attribute to true.

(Download Code)

import com.imsl.chart.*;

public class SampleHeatmap extends JFrameChart {
    
    public SampleHeatmap() {
        Chart chart = getChart();
        AxisXY axis = new AxisXY(chart);
        double xmin = 0.0;
        double xmax = 5.0;
        double ymin = 0.0;
        double ymax = 4.0;
        double zmin = 0.0;
        double zmax = 100.0;
        double data[][] = {
            {23, 48, 16, 56},
            {89, 74, 54, 32},
            {12, 45, 18,  9},
            {72, 15, 42, 92},
            {63, 36, 78, 29}
        };
        Heatmap heatmap = new Heatmap(axis, xmin, xmax, ymin, ymax,
            zmin, zmax, data, Colormap.BLUE_RED);
        heatmap.getHeatmapLegend().setPaint(true);
    }
    
    public static void main(String argv[]) {
        new SampleHeatmap().setVisible(true);
    }
}