---
name: "build-astrometry-index"
section: "1"
platform: "linux"
package: "astrometry.net"
version: "0.97+dfsg-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/build-astrometry-index"
---

# build-astrometry-index(1)

Create astrometry.net index files

## NAME

build-astrometry-index - Create astrometry.net index files

## SYNOPSIS

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

## DESCRIPTION

**build-astrometry-index** takes a FITS catalog table containing at least *RA***,** *DEC*, and *magnitude* columns and converts it into an index file that can be used by the astrometry.net programs like **solve-index** (1).

## OPTIONS

- **-i** *catalog*

  Input FITS catalog: source RA,DEC, etc.

- **-e** *extension*

  FITS extension to read when **-i** is specified.

- **-1** *index*

  Share another index's stars (alternatively to **-i**/**-e**).

- **-o** *file*

  Output filename for index

- **-N** *nside*

  Healpix Nside for quad-building

- **-l** *size*

  Minimum quad size (arcminutes)

- **-u** *size*

  Maximum quad size (arcminutes)

- **-P** *number*

  Use 'preset' values for **-N**, **-l**, and **-u**. 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*

  Sort column (default: assume the input file is already sorted)

- **-f**

  Sort in descending order (eg, for FLUX); default 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 no deduplication

- **-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.

- **-I** *id*

  Set the unique ID of this index

- **-M**

  In-memory (don't use temp files)

- **-T**

  Don't delete temp files

- **-t** *dir*

  Use this temp directory (default: /tmp)

- **-v**

  Add verbosity.

## AUTHOR

The Astrometry.net team. Principal investigators are David W. Hogg (NYU) and Dustin Lang (CMU).

## SEE ALSO

hpsplit (1), solve-field (1)\
 For a tutorial, see http://astrometry.net/doc/build-index.html