Graph plotting in Raspberry Pi using GNUplot

Gnuplot in Raspberry Pi 

Raspberry Pi has been used  for interfacing different types of sensors. Signals from these sensors are stored in a file, generally this file is called data file. Graphical representation of these data offer better visualisation. Here I am going to explain How these data file can be converted into graph using a tool called gnuplot. Install gnuplot in your raspberry pi using apt-get.


first of all create a data file with name data.dat

sudo nano data,dat

and make two column with some data in it

save it with ctrl X then Y

open gnuplot from terminal  by entering gnuplot in terminal. gnuplot will open with its prompt

This is a gnuplot command prompt. From here we will plot the data from data.dat file.

In gnuplot command line enter

plot 'data.dat' with lines and we get our data plotted as following

Set title to this plot by entering

set title 'graph'

plot 'data.dat' with lines

 Lets add some more things to graph. Enter the command as I had shown in figure below

 In this way we can do many things with this plot. In above figure 1:2 represents first column as X axis and second column as Y axis.

Lets add one more column to our data file.
sudo nano data.dat

We can plot multiple graph in a single gnuplot window, Since we are plotting 2D graphs, plotting would require two columns.  Have a look at  figure below and it is self explanatory

Ok we have seen how to plot from a data file.

But how to plot a graph from two different data file. To understand this, create another data file with name data1.dat

sudo nano data1.dat

open gnuplot and follow the figure below, it is just simple as that

Fine, now we know how to plot from two different data files

But always opening gnuplot from terminal is not always desirable. It mean we can invoke gnuplot from our program and can pass gnuplot commands to it. Here is a simple script in C

sudo nano gp.c

compile and run it with

gcc gp.c
sudo ./a.out

you will get your plot open .To add more functionality just pass more gnuplot command through fprintf.

gnuplot is open source and fully documented. Go to the official page to explore more options.