astrometry.js

Extract star pixel coordinates from a FITS image using JavaScript (supported on Node.js and your Browser)

image2xy

A port of the blind image2xy solver utility from astrometry.net using Emscripten.

Install (Node.js)

npm install astrometry.js

Usage

Read a FITS image file into a buffer (or Uint8Array in the browser, see browser example below))

const fs = require('fs');
const buf = fs.readFileSync('./example.fits');

const image2xy = require('astrometry.js').image2xy;

const result = image2xy(buf, { verbose: true, extension: 0 });

Install (Browser)

<script src="https://cdn.jsdelivr.net/npm/astrometry.js"></script>

Usage

You'll need to do a little bit of work to get a file buffer on the browser.

var reader = new FileReader();

reader.onload = function (e) {
    // Get the image file as a buffer
    var buf = new Uint8Array(e.currentTarget.result);

    // Get a fits file buffer containing a star list
    const results = astrometry(buf, { verbose: true, extension: 0 });
};

reader.readAsArrayBuffer(file);

Example

The following shows an example output.

const result = image2xy(buf, { verbose: true, extension: 0 });

>   infile=fits_buf.fits
    outfile=fits_buf.xy.fits
    nhdus=1
    Got naxis=2, na1=4096, na2=4096
    simplexy: nx=4096, ny=4096
    simplexy: dpsf=1.000000, plim=8.000000, dlim=1.000000, saddle=5.000000
    simplexy: maxper=1000, maxnpeaks=10000, maxsize=2000, halfbox=100
    simplexy: median smoothing...
    simplexy: measuring image noise (sigma)...
    Sampling sigma at 42025 points
    Nsigma=0.7, s=13.132
    simplexy: found sigma=13.132.
    simplexy: finding objects...
    simplexy: found 734 blobs
    simplexy: finding peaks...
    simplexy: found 743 sources.

Options

You may use the same options that image2xy supports by providing the flags directly, or you may use the following human friendly versions.

Options List

|Option|Flag|Type|Description| |------|----|----|-----------| |help|'h'| boolean | Print available options and usage instructions| |verbose|'v'| boolean | Print verbose messages| |extension|'e'| number | Read from a single FITS extension| |downsampleFactor|'D'| number | Downsample, if necessary, by this many factors of two| |medianFilteringScale|'s'| number | Set median-filter box size (default 100 pixels)| |psfWidth|'w'| number | Set Gaussian PSF sigma (default 1 pixel)| |noiseLevel|'g'| number | Set image noise level| |peakSigma|'p'| number | Set significance level of peaks (default 8 sigmas)| |saddleLevel|'a'| number | Set saddle level joining peaks (default 5 sigmas)| |disableBackgroundSubtraction|'b'| boolean |Don't do (median-based) background subtraction| |backgroundLevel|'G'| number | Subtract this 'global' background value; implies -b| |outputFilename|'o'| filename | Write XYlist to given filename.| |backgroundSubtractedImageName|'S'| filename | Save background-subtracted image to this filename (FITS float image)| |backgroundImageName|'B'| filename | Save background image to filename| |smoothedImageName|'U'| filename | Save smoothed background-subtracted image to filename| |maskImageName|'M'| filename | Save mask image to filename| |blobImageName|'C'| filename | Save connected-components image to filename|