Operation/centroiding

[capetillo]

FEATURE: Centroiding

Background:
BANZAI does not have a centroid for all targets. To find centroids for the excluded target, we obtained the logic from AstroimageJ, which uses the Howell method to obtain the centroid.

Implementation
The user clicks on a position and sends the clicked x and y as well as radius, r_back1 (the inner annulus), r_back2 (outer annulus) to the backend. These are first scaled into FITS pixel space and then the local background is estimated from the annulus around the selected source, and iteratively refines the source center using the flux-weighted signal in the centroid window.
The /centroiding endpoint returns x and y as the centroid position. It also returns background, which is the average per pixel signal in that surrounding area, and peak, which is the brightest source signal above that background.
When the FITS header contains a valid WCS solution, we eturn ra and dec by converting the centroided FITS pixel position into sky coordinates. Otherwise those fields are null.
If plane background removal is enabled in the frontend, centroiding does not assume the background is the same everywhere near the source. It fits a simple tilted plane to the pixels in the background annulus and subtracts that changing background model during centroiding.

NOTE
I couldn't find a small FITS file so I couldn't write a test for that

[talister]

@capetillo What we've done for testing this sort of stuff is make a postage stamp cutout around a random star of interest and write this to a new FIST file for testing e.g.

from astropy.io import fits

hdul = fits.open('some file.fits')
cutout = hdul['SCI'].section[200:300, 200:300]

new_hdul = fits.PrimaryHDU(cutout, hdul[0].header)

new_hdul.writeto('cutout.fits', checksum = True)

This will make a 100x100 cutout around (250,250) - alter this to center on the object of interest in your test data FITS file

[jnation3406]

I can't comment on the math but seems fine. I'm not sure I like the super verbose line per param of function definitions but its a personal preference thing so if you like it it's fine.

[jnation3406]

this is some advanced pythoning, I had to lookup what this does.