Hi, does anyone know how I can achieve drawing triangle on level sets of some 3d function (something like on this image in gnuplot? When I tried doing this after reading some tutorials: gnuplot> set border 15 front linetype -1 linewidth 1.000 gnuplot> set logscale z 10 gnuplot> set view map gnuplot> set isosamples 60, 60 gnuplot> unset surface gnuplot> set contour base gnuplot> unset clabel gnuplot> set style data lines gnuplot> set ticslevel 0 gnuplot> set noztics gnuplot> set title "Trwa symulacja" gnuplot> set xlabel "x" gnuplot> set xrange [ * : * ] noreverse nowriteback gnuplot> set ylabel "y" gnuplot> set zlabel "" gnuplot> set yrange [ * : * ] noreverse nowriteback gnuplot> set zrange [ * : * ] noreverse nowriteback gnuplot> splot [-10.5:10.5] [-10.5:10.5] x**2 +y**2 with lines lc rgb "#000000" notitle,\ >'-' with lines notitle input data ('e' ends) > 5.39703780733842 0.424994542694183 29.3086374551602 input data ('e' ends) > -4.80045950473308 -8.66307635892326 98.0933034571172 input data ('e' ends) > -3.56740563691939 3.31903046267993 23.7423461905216 input data ('e' ends) > 5.39703780733842 0.424994542694183 29.3086374551602 input data ('e' ends) > e But I'm still getting warning: "Cannot contour non grid data. Please use "set dgrid3d".".