8.9 Contour

gnuplot 提供 contour 的功能。contour 画在 x、y 平面上，或曲面本身。 只要输入指令 set contour 后，即可绘出 contour。contour 可由设定参数 cntrparam 而改变 contour 外貌。

set samples 20
set isosamples 21
set xlabel "x axis" -5,-2
set ylabel "y axis" 4,-1
set zlabel "z axis"
set title "contour plot"
set contour
splot x*y

set samples 20
set isosamples 21
set xlabel "x axis" -5,-2
set ylabel "y axis" 4,-1
set zlabel "z axis"
set cntrparam levels 20
set title "contour plot (more contours)"
set contour
splot x*y

set samples 20
set isosamples 21
set xlabel "x axis" -5,-2
set ylabel "y axis" 4,-1
set zlabel "z axis"
set title "contour plot (every 10, starting at -100)"
set contour
set cntrparam levels incr -100,10,100
splot x*y

set samples 20
set isosamples 21
set xlabel "x axis" -5,-2
set ylabel "y axis" 4,-1
set zlabel "z axis"
set contour
set cntrparam levels disc -75,-50,0
set title "contour plot (at -75, -50, 0)"
splot x*y

set xrange [-3:3]
set yrange [-3:3]
set samples 6
set isosamples 6
set cntrparam levels 5
set title "low resolution (6x6)"
set contour
splot x*y

set xrange [-3:3]
set yrange [-3:3]
set xlabel "x axis" -5,-2
set ylabel "y axis" 4,-1
set zlabel "z axis"
set samples 6
set isosamples 6
set contour
set cntrparam order 4
set cntrparam bspline
set title "low resolution (6x6) using bspline approx."
splot x*y