Including solid and dashed contours in gnuplot - gnuplot

Question

i have the following in a gnuplot script:
set pm3d
unset surface
set pm3d map
set style line 1 lt 1 lc rgb "white"
set style line 2 lt 1 lc rgb "white"
set style line 3 lt 1 lc rgb "white"
set style line 4 lt 1 lc rgb "red"
set style line 5 lt 1 lc rgb "blue"
set style line 6 lt 2 lc rgb "white"
set style line 7 lt 2 lc rgb "white"
set style line 8 lt 2 lc rgb "white"
set style line 9 lt 2 lc rgb "white"
set style increment userstyles
set contour base
set cntrparam levels 8
set cntrparam levels discrete -8*0.0004946, -6*0.0004946, -4*0.0004946, -2*0.0004946, -2*0.0004946, 4*0.0004946, 6*0.0004946, 8*0.0004946
set nokey
splot '/data/ltl21/Data/PDB/HDFNI/BlindSurvey/imageresults/spectrum/HDF1map:189.20135-62.20442' u 1:2:3
Such that, i would like to have dashed contours for negative values, and solid contours for positive values. I can change the colour of contours with the above fine, though i want them to all be white, but it doesn't seem to use lt at all, it just picks its own line style and uses that..
Does anyone know how to specify the linetype for individual contours?
Cheers

Answer 1

Same question just appeared to me. Here is a nice workaround I found at http://www.gnuplot.info/faq/faq.html :
gnuplot> # An example. Place your definition in the following line:
gnuplot> f(x,y) = y - x**2 / tan(y)
gnuplot> set contour base
gnuplot> set cntrparam levels discrete 0.0
gnuplot> unset surface
gnuplot> set table ’curve.dat’
gnuplot> splot f(x,y)
gnuplot> unset table
gnuplot> plot ’curve.dat’ w l
Use splot with your standard options. You can save more than one contour in one file. Each contour in the same file will be plotted in the same style.
You can set your plot options as usual: linestyle, linetype etc. That's how I used it:
gnuplot> set cntrparam levels discrete 0,1,2,3
gnuplot> set style line 1 lt 2 lw 4 lc rgb "cyan"
gnuplot> set table 'mycontours.dat'
gnuplot> splot 'mydata.dat' matrix
gnuplot> unset table
gnuplot> plot 'mycontours.dat' ls 1
It returned 4 dashed cyan contours in epslatex. It seems you need to save to different files for different contour styles (or edit the file by hand).

Answer 2

multiplot may be used to address this issue:
set pm3d
unset surface
set pm3d map
set view map
set key center rmargin
set dgrid3d 15,31
set hidden3d
set contour base
set nosurface
set grid lw 1 lc rgb 'gray'
f(x,y) = x*y
set nokey
set cntrparam levels discrete 2, 4, 6, 8
set linetype 1 lc rgb '#0042ad' lw 1.3
set linetype 2 lc rgb '#0060ad' lw 3.1
set linetype 3 lc rgb '#007cad' lw 31
set linetype 4 lc rgb '#0099ad' lw 0.31
set cntrlabel start 25 interval -1 font 'arial, 1'
set style textbox noborder
set multiplot
splot f(x,y) w l title ''
unset pm3d
set linetype 1 lc rgb '#00ada4' lw 2 dashtype 2
# notice how changing 'lw' or 'dashtype' does not have any effect after first use:
set linetype 2 lc rgb '#00ad88' lw 1 dashtype 1
set linetype 3 lc rgb '#00ad6b' lw 3 dashtype 4
set linetype 4 lc rgb '#eeeeee' lw 4 dashtype 3
set cntrparam levels discrete -8, -6, -4, -2
splot f(x,y) w l
unset multiplot
Unsetting pm3d is crucial or it will draw over the lines from the first splot command.