Contour plot gnuplot

Contour plot

To create a contour plot like this two script files are needed. First of all a contour.gnu gnuplot file which plots the data and then contour.sh bash file which edits a temporary output file.

Steps in gnuplot:

1. Write data into temporary file
2. Write contour lines into temporary file
3. Edit temporary file with contour.sh
4. plot the edited data

Contour.sh

 #!/bin/bash  
 gawk -v d=$2 -v w=$3 -v os=$4 'function abs(x) { return (x>=0?x:-x) }  
   {  
       if($0~/# Contour/) nr=0  
       if(nr==int(os+w/2) && d==0) {i++; a[i]=$1; b[i]=$2; c[i]=$3;}  
       if(abs(nr-os-w/2)>w/2 && d==1) print $0  
       nr++  
   }  
   END {  if(d==0) {  
           for(j=1;j<=i;j++)  
           printf "set label %d \"%g\" at %g, %g centre front\n", j, c[j], a[j], b[j]  
       }  
   }' $1  

d: which option (0: set labels, 1: give data back where no label is)
w: width
os: offset

Contour.gnu

 
 # Step 1
 set xrange [-5:0]  
 set yrange [2:5]  
 set isosample 150, 150  
 set table 'test.dat'  
 splot sin(1.3*x)*cos(.9*y)+cos(.8*x)*sin(1.9*y)+cos(y*.2*x)  
 unset table  
 # Step 2
 set cont base  
 set cntrparam level incremental -3, 0.5, 3  
 unset surf  
 set table 'cont.dat'  
 splot sin(1.3*x)*cos(0.9*y)+cos(.8*x)*sin(1.9*y)+cos(y*.2*x)  
 unset table  
 reset
 # Step 3 and 4
 set xrange [-5:0]  
 set yrange [2:5]  
 unset key  
 set palette rgbformulae 33,13,10  
 load '<./contour.sh cont.dat 0 20 0'  
 plot 'test.dat' w ima, '<./contour.sh cont.dat 1 20 0' w l lt -1 lw 1.5  

Step 1:

Surface data of the function "sin(1.3*x)*cos(.9*y)+cos(.8*x)*sin(1.9*y)+cos(y*.2*x)" is plotted into "test.dat" in the x- and y-range given.

Step 2:

By using "set cont base" only the contour data of the function is written to the file "cont.dat"

Step 3:

By loading the contour.sh script the contour data in cont.dat is read and the labels for gnuplot are created.

Step 4:

The plot command plots first the data as an image and adds to that the modified contour data (modified by contour.sh)


adapted from http://gnuplot-tricks.blogspot.com/2009/07/maps-contour-plots-with-labels.html