Ionică Bizău

Pi Day, Raspberry Pi and Command Line

Everyone knows (or should know) what the Pi number is. Basically, its value is defined by the division of a circle circumference to its diameter. That's the Pi number! The nice thing about it is its irrational nature. That means it has a lot an infinity of decimals.

Usually, Pi is approximated as 3.14. And today is 14th of March! So, happy Pi day! :)

I have a Raspberry Pi computer around, and I was thinking to use two of my libraries to create something nice: displaying the Raspberry Pi's logo and the Pi number in the command line: it's funny how it basically stands for Raspberry Pi (the raspberry image and the pi number). I wanted one more thing: using the pi number decimals in the output characters. Here's the result (see below how I did it):

How I did it

To display the images in the terminal, I used image-to-ascii. To pass different image urls, I decided to use command line arguments.

To get the first n decimals of the pi number, I used another module I created this time last year: pi. This module returns a good approximation of pi:

const pi = require("pi");

// => '3.141592653'

So, I created a file named index.js and I wrote the following stuff in it (follow the inline comments):

// Require the needed dependencies
// `pi` will be used to return the first `n` decimals of pi
const pi = require("pi")

      // image-to-ascii for displaying the images in the terminal
    , img = require("image-to-ascii")

      // We use this module to stringify the pixel matrix after
      // modifying the internal data (basically, the characters)
    , stringify = require("asciify-pixel-matrix")

// Take the image url/path from the command line arguments
img(process.argv[2], {
    // We turn off the stringifying, since we really want to do
    // some changes before displaying the images
    stringify: false
  , concat: false
}, (err, converted) => {
    // Handle the errors
    if (err) { return console.error(err); }

    // `converted` is an array of arrays (in fact, a matrix of pixels)
    // We use the `converted` matrix to know how many decimals we
    // need: width x height
    // `piNumber` will be a string in this format: "3.14...." (with a
    // lot of decimals)
    var piNumber = pi(converted.length * converted[0].length);

    // We will use this `i` variable to get the current index
    var i = -1;

    // For each row in the matrix
    converted.forEach(cRow => {
        // ...and for each pixel in the row
        cRow.forEach(px => {
            // ...update the character using a pi decimal, in order
            px.char = piNumber[i = ++i % piNumber.length];

    // Finally, stringify everything and display the result! Yay!

The requirements to run this script are:

  • Node.js (I installed it on my Raspberry Pi using nvm)
  • graphicsmagick: sudo apt-get install graphicsmagick (this is optional, kind of: if it's not available image-to-ascii will compile some C/C++ stuff, but it will probably take a long time)
  • …and of course the npm dependencies: npm i image-to-ascii pi asciify-pixel-matrix

Happy Pi Day!

PS: I posted this article using my Raspberry Pi, connected to the Internet and using a 7" display. Just perfect. :)

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