Gnuplot , pm3d with contour lines

Question

i am 3d plotting a matrix with some values, and i need to add contour lines to the plot, is there a simple gnuplot command to do this?

I tried the command: \"set contou

Answer 1

What you are missing is to tell gnuplot where to put the contours. This is done via the set cntrparam levels incr -0.3,0.1,0.5 command which means: start at -0.3 and trace a contour every o.1 up to 0.5.

AFAIK if you want to make contours all black, you have to save the contour lines in a temporary file (here contour.txt).

So your script would be

reset
set contour
unset surface
set cntrparam levels incr -0.3,0.1,0.5

set view map
set xrange [0:30]
set yrange [0:30]

set dgrid3d 100,100,4

set table "contour.txt"
splot 'test.txt'
unset table

unset contour
set surface
set table "dgrid.txt"
splot 'test.txt'
unset table

reset
set pm3d map
unset key
set palette defined (0 '#352a87', 1 '#0363e1',2 '#1485d4', 3 '#06a7c6', 4 '#38b99e', 5 '#92bf73', 6 '#d9ba56', 7 '#fcce2e', 8 '#f9fb0e')
set autoscale fix
set grid

splot 'dgrid.txt' w pm3d, 'contour.txt' w l lc rgb "black"

which gives you this:

Note:

you can get rid of interpolation file (dgrid.txt) if you format a bit your datafile by leaving a blank line after each row (i.e. every 30 datapoints) because they are already mesh-ordered.

This could be done also with a awk script. But I'm too lazy to look into it...

The rest will remain the same and will work as expected.

here is how it should look like :

In which case the script would simply become:

set pm3d map impl
set contour
set style increment user
do for [i=1:18] { set style line i lc rgb "black"}
set cntrparam levels incr -0.3,0.1,0.5
set palette defined (0 '#352a87', 1 '#0363e1',2 '#1485d4', 3 '#06a7c6', 4 '#38b99e', 5 '#92bf73', 6 '#d9ba56', 7 '#fcce2e', 8 '#f9fb0e')
set autoscale fix
splot 'test.txt' w pm3d notitle

with no need of ntermediate file and with better contour since data in not interpolate by gridded: