Populate Celestron Origin FITS header metadata using info.json

origin_metadata.py

#!/usr/bin/env python
#
# This script populates metadata in the headers of FITS files produced by a Celestron Origin
# telescope, using information from an accompanying JSON file
#
# Author: @cgobat

import json
import argparse
import numpy as np
import datetime as dt
from pathlib import Path
from astropy.io import fits


def update_header(fits_file: Path, info_json: Path) -> None:

    info = json.loads(info_json.read_bytes())
    info = info.get("StackedInfo", {})
    capture_time = dt.datetime.fromisoformat(info["dateTime"])
    capture_time = capture_time.astimezone(dt.UTC)
    ra_rad, dec_rad = info["celestial"]["first"], info["celestial"]["second"]
    ra_deg, dec_deg = np.rad2deg(ra_rad), np.rad2deg(dec_rad)

    with fits.open(fits_file, mode="update") as f:
        h = f[0].header

        h["TELESCOP"] = ("Celestron Origin", "Telescope name")
        h["INSTRUME"] = ("Celestron Origin", "Instrument name")
        h["APERTURE"] = (152., "[mm] Aperture diameter")
        h["FOCALLEN"] = (335., "[mm] Focal length")
        h["BAYERPAT"] = (info["bayer"].upper(), "Bayer (CFA) pattern")
        h["FILTER"]   = (info["filter"], "Filter name")
        h["CCD-TEMP"] = (info["captureParams"]["temperature"], "[degC] Sensor temperature")
        h["EXPOSURE"] = (info["captureParams"]["exposure"], "[s] Per-frame exposure time")
        h["BINNING"]  = (info["captureParams"]["binning"], "Camera binning (1 for 1x1, 2 for 2x2)")
        h["ISO"]      = (info["captureParams"]["iso"], "ISO (gain) setting")
        h["DATE-OBS"] = (capture_time.strftime("%Y-%m-%dT%H:%M:%S"), "UTC time of observation")
        h["OBJECT"]   = (info["objectName"], "Target name")
        h["RA"]       = (ra_deg, "[deg] Nominal right ascension")
        h["DEC"]      = (dec_deg, "[deg] Nominal declination")
        h["LATITUDE"] = (info["gps"]["latitude"], "[deg] Site latitude")
        h["LONGITUD"] = (info["gps"]["longitude"], "[deg] Site longitude")


if __name__ == "__main__":

    parser = argparse.ArgumentParser()
    parser.add_argument("fits_files", nargs="+", type=Path, help="FITS file(s) to process/update")
    parser.add_argument("-i", "--info", required=True, type=Path, help="JSON file containing capture metadata")
    args = parser.parse_args()

    for file in args.fits_files:
        update_header(file, args.info)
        print(f"Updated {file}")