Setting margins in gnuplot with respect to graph coordinates and not screen

Question

I am trying to plot a second plot inside of my main one. I have specific coordinates for where I would like to place my second plot with respect to the first plot. For example, I want the left margin of the second plot to be on the x=2 line, the right margin to be on the x=8 line and so on as seen on the example image. Currently, I accomplish this by trial and error. I place the margins of the second plot manually until I am satisfied with their locations. However this is time consuming and I am sure there is a smarter way of doing it.

Answer 1

You could impose prescribed margins (in screen units) on the parent plot and then calculate the margins (also in screen units) of the inset from known x/y ranges of the parent plot and required inset position:

set terminal pngcairo enhanced font ",16"
set output "fig.png"

fig_lmargin = 0.2
fig_rmargin = 0.9
fig_bmargin = 0.2
fig_tmargin = 0.9

p1_xMin = 0.
p1_xMax = 10.
p1_yMin = 0.
p1_yMax = 1.

p2_xMin = 0.
p2_xMax = 0.7
p2_yMin = 0.
p2_yMax = 1.

inset_xMin = 2.
inset_xMax = 8.
inset_yMin = 0.25
inset_yMax = 0.75

set multiplot

set lmargin at screen fig_lmargin
set rmargin at screen fig_rmargin
set tmargin at screen fig_tmargin
set bmargin at screen fig_bmargin

set xr [p1_xMin:p1_xMax]
set yr [p1_yMin:p1_yMax]

set linetype 42 lc rgb '#333333' dt 3
set arrow from inset_xMin,p1_yMin to inset_xMin,p1_yMax nohead lt 42
set arrow from inset_xMax,p1_yMin to inset_xMax,p1_yMax nohead lt 42
set arrow from p1_xMin,inset_yMin to p1_xMax,inset_yMin nohead lt 42
set arrow from p1_xMin,inset_yMax to p1_xMax,inset_yMax nohead lt 42

plot x

p1_widthScreen = fig_rmargin - fig_lmargin
p1_widthPlot = p1_xMax - p1_xMin
p1_heightScreen = fig_tmargin - fig_bmargin
p1_heightPlot = p1_yMax - p1_yMin

unset arrow

set lmargin at screen fig_lmargin + (inset_xMin - p1_xMin)/p1_widthPlot*p1_widthScreen
set rmargin at screen fig_lmargin + (inset_xMax - p1_xMin)/p1_widthPlot*p1_widthScreen
set bmargin at screen fig_bmargin + (inset_yMin - p1_yMin)/p1_heightPlot*p1_heightScreen
set tmargin at screen fig_bmargin + (inset_yMax - p1_yMin)/p1_heightPlot*p1_heightScreen

plot x

EDIT:

Using the technique outlined in the answer linked by @Christoph, one can simplify the script above as:

set terminal pngcairo enhanced font ",16"
set output "fig.png"

xMin = 0.
xMax = 10.
yMin = 0.
yMax = 1.

inset_xMin = 2.
inset_xMax = 8.
inset_yMin = 0.25
inset_yMax = 0.75

set multiplot

set xr [xMin:xMax]
set yr [yMin:yMax]

set linetype 42 lc rgb '#333333' dt 3
set arrow from inset_xMin,yMin to inset_xMin,yMax nohead lt 42
set arrow from inset_xMax,yMin to inset_xMax,yMax nohead lt 42
set arrow from xMin,inset_yMin to xMax,inset_yMin nohead lt 42
set arrow from xMin,inset_yMax to xMax,inset_yMax nohead lt 42

plot x

lmargin = GPVAL_TERM_SCALE * GPVAL_TERM_XMIN / (1.*GPVAL_TERM_XSIZE)
rmargin = GPVAL_TERM_SCALE * GPVAL_TERM_XMAX / (1.*GPVAL_TERM_XSIZE)
bmargin = GPVAL_TERM_SCALE * GPVAL_TERM_YMIN / (1.*GPVAL_TERM_YSIZE)
tmargin = GPVAL_TERM_SCALE * GPVAL_TERM_YMAX / (1.*GPVAL_TERM_YSIZE)

widthScreen = rmargin - lmargin
heightScreen = tmargin - bmargin
widthPlot = xMax - xMin
heightPlot = yMax - yMin

unset arrow

set lmargin at screen lmargin + (inset_xMin - xMin)/widthPlot*widthScreen
set rmargin at screen lmargin + (inset_xMax - xMin)/widthPlot*widthScreen
set bmargin at screen bmargin + (inset_yMin - yMin)/heightPlot*heightScreen
set tmargin at screen bmargin + (inset_yMax - yMin)/heightPlot*heightScreen

set xr [0:0.7]
set yr [0:1.0]

plot x