# set terminal png transparent nocrop enhanced font arial 8 size 420,320 
# set output 'contours.20.png'
set samples 25, 25
set isosamples 26, 26
set contour base
set cntrparam bspline
set cntrparam levels auto 10
set style data lines
set title "3D gnuplot demo - contour of data grid plotting" 0.000000,0.000000  font ""
set xlabel "X axis" -5.000000,-2.000000  font ""
set xrange [ * : * ] noreverse nowriteback  # (currently [0.00000:15.0000] )
set ylabel "Y axis" 4.000000,-1.000000  font ""
set yrange [ * : * ] noreverse nowriteback  # (currently [0.00000:15.0000] )
set zlabel "Z axis" 0.000000,0.000000  font ""
set zrange [ -1.20000 : 1.20000 ] noreverse nowriteback
splot "glass.dat" using 1