gnuplot: contour and heatmap from two different files in the same splot

Question

I am trying to plot two 2D scalar quantities, one as a heatmap and one as superimposed contour, using the following code:

set contour base
set cntrparam levels incremental 0,0.25,1.25
unset surface
set table cont2.dat
splot 'vr245.gnu'
unset table
reset
set xrange [1:215]
set yrange [0:3.1415925025940E+00]
set cbrange [7:17]
unset key
set view map
set palette rgbformulae 33,13,10
splot 'f_aveFe_245.gnu' u 1:2:3 with pm3d, "cont2.dat" u 1:2:3 w l

Result produced by gnuplot

As you can see the contour has artifacts on the left. How can I fix this problem? Thank you!

Input files are here.

Answer 1

It's actually quite interesting. The problem seems to arise for a particular contour corresponding to the level of 1.25. I think I isolated the issue to the following.

Let's assume that we have a simple datafile as

215  2.55865  1.25 
212.185  2.56004  1.25 
215  2.87839  1.25 

215  0.2632  1.25 
212.185  0.252052  1.25 
215  0.582938  1.25

now, the gnuplot command(s)

unset key
set view map

set xr [212:215.5]
set yr [0:3]

set xtics nomirror
set ytics nomirror

splot \
    'file.dat' w lp, \
    '' u 1:2:3:(sprintf("%d", $0)) w labels offset char 0, char -0.5

produce

interestingly, also points 1 and 4 are joined. If the data file is modified as

215  2.55865  1.25 
212.185  2.56004  1.25 
215  2.87839  1.25 
#
215  0.2632  1.25 
212.185  0.252052  1.25 
215  0.582938  1.25

Gnuplot connects only points 2 and 3 as expected:

What seems to help here is to duplicate the blank line, i.e., this file

215  2.55865  1.25 
212.185  2.56004  1.25 
215  2.87839  1.25 


215  0.2632  1.25 
212.185  0.252052  1.25 
215  0.582938  1.25

gives indeed disconnected components:

To apply this in your script, one might invoke for example gawk and merely duplicate all blank lines in the file with calculated contours:

set terminal pngcairo
set output 'fig.png'

set contour base
set cntrparam levels incremental 0,0.25,1.25
unset surface
set table 'cont2.dat'
splot 'vr245.gnu'
unset table
reset

set xrange [1:215]
set yrange [0:pi]
set cbrange [7:17]
unset key
set view map
set palette rgbformulae 33,13,10
splot \
    'f_aveFe_245.gnu' u 1:2:3 with pm3d, \
    '<gawk "NF==0{print;} {print;}" cont2.dat' u 1:2:3 w l

which gives

Alternatively, you might fix this by using plot to plot the contours instead of splot:

set terminal pngcairo
set output 'fig.png'

set contour base
set cntrparam levels incremental 0,0.25,1.25
unset surface
set table 'cont2.dat'
splot 'vr245.gnu'
unset table
reset

set xrange [1:215]
set yrange [0:pi]
set cbrange [7:17]
unset key
set view map
set palette rgbformulae 33,13,10

set multiplot

set tmargin at screen 0.9
set lmargin at screen 0.1
set rmargin at screen 0.8
set bmargin at screen 0.1

splot \
    'f_aveFe_245.gnu' u 1:2:3 with pm3d

unset xtics
unset ytics
unset border
unset key
plot \
    'cont2.dat' w l

Answer 2

You can selectively switch on or off contouring and plotting of the surface for individual plots in a single splot. Define both pm3d and contours in the script, deactivate contours for the first and surface for the

reset
set contour base
set cntrparam levels incremental 0,0.25,1.25
set cntrlabel onecolor
set autoscale xfix
set autoscale yfix
set cbrange [7:17]
unset key
set view map
set palette rgbformulae 33,13,10
splot 'f_aveFe_245.gnu' u 1:2:3 with pm3d nocontour, \
    'vr245.gnu' u 1:2:3 w l lc rgb "black" nosurface