How to add in gnuplot a vertical line on a 3D splot?

Question

I have a 3D plot with the option:
set view map
And I would like to add a vertical line from (30,0) to (30,20), I tried:

set arrow from 30,0 to 30,20 nohead lc rgb 'red'
splot 'data.csv' using 1:2:3 with pm3d

But I don't see any line, what am I doing wrong ? This is the image on which I would like to add the vertical line

Answer 1

The "trick" is front. Check help layers.

Code:

### arrow on top of map view
reset session

set view map
set arrow 1 from 50,0 to 50,20 nohead lc rgb 'red' front

set xrange[0:140]
set yrange[0:20]

splot x*y/3000 w pm3d notitle
### end of code

Result: