jsFITS

FITS is the Flexible Image Transport System and is widely used in astronomy for holding observation data. There are many FITS I/O libraries available in a variety of languages. This is an attempt to build a FITS library for Javascript to allow FITS files to be displayed in a modern web browser. Given that FITS files have no compression they are quite large so I imagine this library will be more useful when run locally. By displaying the image using

Dependencies

For this library to work it has two dependencies:

binaryajax.js -- this does the XMLHttpRequest and the bit extraction. It is created by Jacob Seidelin and is only about 6.2 kB;
excanvas.js -- this is used to allow canvas support on Internet Explorer (41.6 kB).

Limitations

Due to web browser cross-domain security issues, any FITS file you want to read must be hosted on the same domain as the code.

Usage

You need to include the appropriate Javascript files:

<script src="https://github.com/slowe/jsFITS/raw/master/binaryajax.js"></script>
<script src="https://github.com/slowe/jsFITS/raw/master/excanvas.js"></script>
<script src="https://github.com/slowe/jsFITS/raw/master/fits.js"></script>

Following those you can define your FITS object:

var fits = new FITS();

Next we define what happens on load:

fits.bind("load",function(){

    // Display some values
    document.getElementById('bitpix').innerHTML = this.header.BITPIX;
    document.getElementById('depth').innerHTML = this.depth;
    document.getElementById('z').value = 0;

    this.draw("FITSimage")  // Draw the image to the element with id=FITSimage
})

We can also bind some other events (which are chainable) e.g.:

fits.bind("click",function(e){
    e.y = this.height - e.y
    var value =this.image[e.y*this.width+e.x];
    document.getElementById('status').innerHTML ='click=('+ e.x+','+e.y+')='+value;
}).bind("mousemove",function(e){
    e.y = this.height - e.y
    var value =this.image[e.y*this.width+e.x];
    document.getElementById('status').innerHTML ='move=('+ e.x+','+e.y+')='+value;
})

Finally, load the FITS file. We've already defined the load event above:

fits.load("WFPC2u5780205r_c0fx.fits");

FITS files

The example makes use of several FITS files. You can get these at:

M51 (taken with Faulkes Telescope North operated by LCOGT),
M108 (taken with Faulkes Telescope North operated by LCOGT).
NGC 2011 (taken with Faulkes Telescope South operated by LCOGT)
NGC 2020 (taken with Faulkes Telescope South operated by LCOGT)
WFPC II 800 x 800 x 4 primary array data cube containing the 4 CCD images (trimmed to 200 x 200 and taken from http://fits.gsfc.nasa.gov/fits_samples.html)

Author

Stuart Lowe works for the Las Cumbres Observatory Global Telescope. LCOGT is a private operating foundation, building a global network of telescopes for professional research and citizen investigations.

Some improvements have been suggested by anonymous contributors.