gnuplot — Basic 3D Plot

By roman10 On March 30, 2012 · Leave a Comment

Previous post covers gnuplot basic 2D plot. This post covers the basics of gnuplot 3D plot.
Most of the 2D plot options apply to 3D plot, one should read the 3D plot post before reading this post.

gnuplot supports splot command for drawing 3D figures and graphs.

There are 3 options specific to 3D plot: isosamples, hidden3d, and surface.

isosamples: controls the number of grid points at which a function will be evaluated when using splot. It is therefore only relevant when plotting functions.

set isosamples {int:xlines} [,{int:ylines}]

hidden3d: use opaque surface rendering. It has the following format:

set hidden3d [offset {int:offset}] [trianglepattern {int:maks}]

offset: used to control the color and line type used for the bottom side of the surface.
trianglepattern: control which lines will be drawn to connect neighboring grid points.

surface: by default, the surface is shown. It can be switched off by using the command,

unset surface

or switch on with the command,

set surface

An Example

Below is a sample 3D plot script,

unset title
#unset key
#unset xtics
#unset ytics
#set format y "%.1t";
#set format x "%.1t";
set title "Test 3D" 0,1
set xlabel "X" -4,-2;
set ylabel "Y" 0,-2;
set zlabel "Z" 4,6;
#set border 0
set hidden3d offset 0
set surface
#set the view angle: one can adjust manually to get the proper value first
#and then modify the value here
set view 80,49 
#set xrange []
#set yrange []
#set zrange []
#set ticslevel 0
#splot '45050.data' u 1:2:3 with lines
splot '$0' using 1:2:3 title "data1" with linespoints, '$1' using 1:2:3 title "data2" with linespoints
#
set term push 
set term png size 800, 600
set output "$2"
replot
set output
set terminal pop

Suppose the file is saved as 3d.pg. And the two data files “3data.dat” and “3data2.dat” are listed below. Note that the data file must follow certain formats, otherwise the plot may not be expected. gnuplot supports two 3D data file formats, we only covers the grid format here. One can refer to reference 1 for more details.

The grid data format supported by gnuplot requires the follows,

each line must contain x and y coordinates and the z value.
data are organized into data blocks. And blocks are separated by a single blank line.
each block must contain all data points for a single row of data points parallel to x axis. Therefore, the x coordinate stays constant at each data block.
all data blocks must contain same number of data points. If the number is not the same, then gnuplot cannot draw a proper surface.

3data.dat

And 3data2.dat