BUILD-ASTROMETRY-INDEX(1)

💖 build-astrometry-index(1) — astrometry.net's very own glow-up machine 💖

okay bestie, sit down, hydrate, because this one is a whole vibe. this is a page from the astrometry.net manual set, and it's genuinely iconic.

✨ NAME ✨

build-astrometry-index — literally the tool that creates astrometry.net index files. no cap, that's the whole job.

🎀 SYNOPSIS 🎀

build-astrometry-index [options] -i catalog -o file -P scale

🌸 DESCRIPTION 🌸

so the way that this works: build-astrometry-index takes a FITS catalog table — and it needs at least RA, DEC, and magnitude columns, ok, those are non-negotiable — and it converts that whole thing into an index file 💅.

and what's the index file for?? it's the thing the astrometry.net programs use, like solve-index (1). it's giving supply chain. one tool makes the index, the others eat it. 🍓

👑 OPTIONS 👑

here we go, the full menu, no skips, no cuts:

• -i catalog — the input FITS catalog: source RA, DEC, etc. this is your raw material, bestie.
• -e extension — which FITS extension to read when you've specified -i.
• -1 index — share another index's stars. this is the alternative route to -i/-e, if you'd rather borrow than build.
• -o file — the output filename for your index. name it something cute, i'm begging.
• -N nside — Healpix Nside for quad-building.
• -l size — minimum quad size, in arcminutes.
• -u size — maximum quad size, in arcminutes.
• -P number — uses 'preset' values for -N, -l, and -u, so you don't have to hand-pick them. the scale-number is the last two digits of the pre-cooked index filename — eg., index-205 is -P 5.
  • -P 0 should be good for images about 6 arcmin in size, and it goes in steps of sqrt(2), so:
  • -P 2 should work for images about 12 arcmin across
  • -P 4 should work for images about 24 arcmin across
  • -P 6 should work for images about 1 degree across
  • -P 8 should work for images about 2 degree across
  • -P 10 should work for images about 4 degree across etc... up to -P 19
• -S column — the sort column. default behaviour is to assume the input file is already sorted, which is a bold assumption, so maybe don't make it.
• -f — sort in descending order (eg, for FLUX); default is ascending (eg, for MAG).
• -A column — specify the RA column name in the input FITS table (default "RA").
• -D column — specify the Dec column name in the input FITS table (default "Dec").
• -B val — cut any object whose sort-column value is less than val; for mags this is a bright limit ✂️.
• -U — Healpix Nside for uniformization (default: same as -n).
• -H big healpix — big healpix; default is all-sky 🌈.
• -s Nside — big healpix Nside; default is 1.
• -m margin — add a margin of margin healpixels; default 0.
• -n sweeps — sweeps (ie, number of stars per fine healpix grid cell); default 10.
• -r radius — deduplication radius in arcseconds; default is no deduplication, so if you want it you gotta ask for it.
• -j jitter — positional error of stars in the reference catalog (in arcsec; default 1).
• -d dimquads — number of stars in a "quad" (default 4).
• -p passes — number of rounds of quad-building (ie, number of quads per healpix cell, default 16).
• -R reuse — number of times a star can be used (default: 8).
• -L max-reuses — make extra passes through the healpixes, increasing the -r reuse limit each time, up to max-reuses.
• -E — scan through the catalog, checking which healpixes are occupied. a lil reconnaissance moment 🔍.
• -I id — set the unique ID of this index. give it an identity, it deserves one 💜.
• -M — in-memory (don't use temp files). speedrun mode.
• -T — don't delete temp files. (the opposite energy of -M, lol.)
• -t dir — use this temp directory (default: /tmp).
• -v — add verbosity. say more, queen.

🫶 AUTHOR 🫶

the Astrometry.net team. principal investigators are David W. Hogg (NYU) and Dustin Lang (CMU). absolute legends, fr fr.

🦋 SEE ALSO 🦋

• hpsplit (1)
• solve-field (1)

and for a tutorial, go look at http://astrometry.net/doc/build-index.html — it's the study guide bestie, use it 📚✨

okay and that's the whole page, you ate it. this was version 0.56, dated July 2015, from the astrometry.net source. slay, bye 👑💖