Question

I’m trying to display a spectogram using JavaPlot with this piece of code:

    PlotStyle style = new PlotStyle();
    style.setStyle(Style.IMAGE);


    DataSetPlot data = new DataSetPlot(points);
    data.setPlotStyle(style);


    JavaPlot plot = new JavaPlot();
    plot.addPlot(data);
    plot.plot();

Where the points are valid as they work when using gnuplot in the command line like this:

 gnuplot --persist -e 'plot "data.dat" w image'

The problem is that the above piece of code doesn’t show any image at all, it is all white. However the previous command works fine, and data.dat contains the points in the exactly same format. No error appears when running the code.

Here is a example of some points data:

0.0 193.0 0.18183826861232413
0.0 194.0 0.2467637036800797
0.0 195.0 0.43531750893288235
0.0 196.0 0.3893599780473012
0.0 197.0 0.3220816458659573
0.0 198.0 0.25389713892289173
0.0 199.0 0.22935136709597423
1.0 0.0 0.23021155472288352
1.0 1.0 0.33383157107150707
1.0 2.0 0.3745792715533692
1.0 3.0 2.028348052193793
1.0 4.0 2.4150235476868978
1.0 5.0 2.4169194327766736
1.0 6.0 1.8633442057577019
1.0 7.0 4.2682342944471054
1.0 8.0 3.22544345282322

And this are the commands sended to gnuplot by JavaPlot:

set multiplot layout 1,2 rowsfirst downwards
_gnuplot_error = 1
plot '-' title 'Datafile 1' with image ; _gnuplot_error = 0
0.0 9.0 6.612583996900796 
1.0 9.0 4.719585678813712 
2.0 9.0 0.5475948495661151 
3.0 9.0 0.7385211622757041 
4.0 9.0 0.711512824841686 
5.0 9.0 3.7572382303712604 
6.0 9.0 1.0818137070547578 
7.0 9.0 0.057188125070687344 
8.0 9.0 0.8218555010675036 
9.0 9.0 5.754170136586405 
e
if (_gnuplot_error == 1) print '_ERROR_'
unset multiplot
quit

For this example I took 10×10 points, so the passed coordinates should be something like:

0.0 0.0 6.612583996900796 
0.0 1.0 4.719585678813712 
0.0 2.0 0.5475948495661151 
0.0 3.0 0.7385211622757041 
0.0 4.0 0.711512824841686 
0.0 5.0 3.7572382303712604 
0.0 6.0 1.0818137070547578 
0.0 7.0 0.057188125070687344 
0.0 8.0 0.8218555010675036 
0.0 9.0 5.754170136586405 
1.0 0.0 6.612583996900796 
1.0 1.0 4.719585678813712 
1.0 2.0 0.5475948495661151 
1.0 3.0 0.7385211622757041 
1.0 4.0 0.711512824841686 
1.0 5.0 3.7572382303712604 
1.0 6.0 1.0818137070547578 
1.0 7.0 0.057188125070687344 
1.0 8.0 0.8218555010675036 
1.0 9.0 5.754170136586405 
...
9.0 9.0 xxxxxxxxxxxxx

It seems that JavaPlot is not iterating the Y coordinates.

Does someone know what am I doing wrong?

Answer 1

As I couldn’t fix that error I finally decided to call gnuplot and pass the points correctly by myself. Here is the piece of code I’ve used to draw the spectogram:

Process p = Runtime.getRuntime().exec("gnuplot --persist");

BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));
String s = "plot '-' title 'Spectogram' w image\n";
writer.write(s);
writer.flush();

for(int m = 0; m < x.length; m++){
   for(int k = 0; k < x[0].length; k++){
       s = m + " " + k + " " + x[m][k] + "\n";
       writer.write(s);  
       writer.flush();
   }
}

s = "e\n";
writer.write(s);
writer.flush();

And it works! 😀