code_gnuplot.txt

D'abord, cela pour plotter tous les points: 
set title "Voyage dans l'espace - plus court chemin"
set yrange [-0.2:1.2]
set xrange [-0.2:1.2]
splot \
  'plot3.txt' using 1:2:3       with lines lc rgb "black" lw 1 notitle,\
  'plot3.txt' using 1:2:3  with points palette pointsize 3.5 pointtype 7,\
  'plot3.txt' using 1:2:3:4     with labels rgb "white" font 'Arial' notitle

puis pour plotter le chemin précis choisi par l'algorithme 
set title "Voyage dans l'espace - plus court chemin"
set yrange [-0.2:1.2]
set xrange [-0.2:1.2]
splot \
  "plot3.txt" using 1:2:3       with lines lc rgb "black" lw 1 notitle,\
  "plot5.txt" using 1:2:3  with lines lc rgb "blue" lw 4 notitle,\
  "plot5.txt" using 1:2:3  with points pointsize 5 pointtype 7,\
  "plot5.txt" using 1:2:3:4     with labels rgb "white" font 'Arial' title "your path"