Extract star pixel coordinates from a FITS image using JavaScript (supported on Node.js and your Browser)
A port of the blind image2xy solver utility from astrometry.net using Emscripten.
npm install astrometry.js
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 });<script src="https://cdn.jsdelivr.net/npm/astrometry.js"></script>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);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.You may use the same options that image2xy supports by providing the flags directly, or you may use the following human friendly versions.
| 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 |