node-fits: a set of (experimental) tools to access FITS files from Node.

FITS is a versatile file format used to store astronomical images and data (http://fits.gsfc.nasa.gov/fits_home.html). This node plugin

Install node.js

Skip if you already installed node.js on your machine.

From: http://yoember.com/nodejs/the-best-way-to-install-node-js/

On Linux (other OS are treated in the previous link):

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.35.1/install.sh | bash

nvm ls-remote
nvm list
nvm install lts/dubnium
nvm use lts/dubnium
nvm alias default lts/dubnium
node -v
npm install -g npm
npm -v
source ~/.nvm/nvm.sh

Install dependecies needed by node-fits:

The node-fits module compiles on GNU/Linux with g++. node-gyp is used as building tool. Other platforms have not been tested yet.

You will need to install the development versions of libpng, libjpeg and libcfitsio. The package names may differ in your distribution. On a debian-based system, the following command should install the required libraries.

sudo apt install g++ libpng-dev libcfitsio-dev 

Install this package

# Cloning and installing dependencies
git clone https://github.com/Nunkiii/node-fits.git
cd node-fits/
npm install

Testing

The test.js file, in the node-fits/test directory, loads an example FITS image file (a galaxy), display all the headers, then creates a PNG and a JPEG snapshots of the image using a custom colormap and pixels intensity cut values. It also shows how to retrieve the image pixel array as a JavaScript ArrayBuffer.

To run the test :

node test.js

It should display headers onthe console and output two images in the test directory.

First the package is loaded and a new fits object constructed. The file is automatically opened for reading if the file name is specified on constructor.

var fits=require("../build/Release/fits");
var f = new fits.file("example.fits"); 

The file can also be specified as the file_name property of the fits object. The file is not opened immediately but will be automatically when needed.

f.file_name="example.fits";

To retrieve the headers, use the get_headers function.

f.get_headers(function(error, headers){

if(error){
  console.log("Bad things happened : " + error);
  return;
}

console.log("FITS Headers : " + JSON.stringify(headers,null,5));

});

Getting data from an image hdu :

f.read_image_hdu(function(error, image){

    if(error){
    console.log("Bad things happened while reading image hdu : " + error);
    return;
        }

if(image){

    console.log("Read image : " + image.width() + ", " + image.height()); 

    var colormap=[ [0,0,0,1,0], [1,0,1,1,.8], [1,.2,.2,1,.9], [1,1,1,1,1] ];
    var cuts=[0,200];

    image.set_colormap(colormap);
    image.set_cuts(cuts);

    var fs=require("fs"),out;

The image.tile() function was initially designed for a image viewer's tile generator but can be used to produce custom PNG/JPEG.

     out = fs.createWriteStream("small.png");
     out.write(image.tile( { tile_coord :  [2,3], zoom :  10, tile_size : [64,64], type : "png" }));
     out.end();

     out = fs.createWriteStream("big.jpeg");
     out.write(image.tile( { tile_coord :  [0,0], zoom :  0, tile_size : [512,512], type : "jpeg" }));
     out.end();

//  image.histogram({ nbins: 350, cuts : [23,65] }, function(error, histo){ .... 

By default cuts are set to min,max and nbins to 200

   image.histogram({}, function(error, histo){ 
    if(error)
        console.log("Histo error : " + error);
else{

    console.log("HISTO : " + JSON.stringify(histo));

        }
     });

Get the image binary data into an arraybuffer :

      var ab=image_data.get_data();
      console.log("image data bytes " + ab.length);