astrometry.js/src/astrometry/doc/UCAC4_guide/README.txt

Extract star pixel coordinates from a FITS image using JavaScript

# Last revision: Dec 20, 2014
# Author: Denis Vida, denis.vida@gmail.com
# NOTICE: This guide was developed on CentOS 6.6, but the author sees no reason why it wouldn't work on any other distribution, provided that you have Python and other prerequisites installed.

# This file is part of the Astrometry.net suite.
# Copyright 2014 Denis Vida.
# The Astrometry.net suite is free software; you can redistribute
# it and/or modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation, version 2.
# The Astrometry.net suite is distributed in the hope that it will be
# useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with the Astrometry.net suite ; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

-------------------------------------------------------------------------------------

PREPARATION:

0.1) Install astrometry.net and make sure you can run astrometry.net commands from the shell. Test by running: hpsplit

0.2) Go to astrometry.net folder (make sure you have the "catalogs" folder present there, if not, get it from astrometry.net github) and run the following commands:
# cd catalogs
# make ucac4tofits 
# mkdir /tmp/UCAC4
# cp ucac4tofits /tmp/UCAC4
# cd /tmp/UCAC4
This will compile the ucac4tofits program, make a working directory in the /tmp and copy the executable to your working directory (where you will be downloading UCAC4 and running the scripts)

-------------------------------------------------------------------------------------
MAIN GUIDE:

1.1) Determine which parts of the sky you need. UCAC4 is divided into 900 individual files and each covers 0.2 degrees of declination. Let's say your observatory covers the sky from +50 to -30 degrees of declination. Edit the get_ucac4.py by modifying the start_dec (starting declination) to +50 and end_dec (ending declination) to -30. Naturally, you will enter the values according to your needs. Save the file.

1.2) copy get_ucac4.py and build-index.py from this directory into the working directory
# cp /path/to/this/directory/*.py /tmp/UCAC4

1.3) Download UCAC4 by running (this will take some time):
# python get_ucac4.py

2) Run this command to convert UCAC4 format to fits tables:
# ./ucac4tofits -N 1 z???.bz2

3) Run this command to split the fits tables into 12 healpix tiles with 1 deg overlap (-m 1):
# hpsplit -o split-%02i.fits -n 1 -m 1 ucac4_???.fits    

4) To trim out unnecessary FITS table columns, run the following commands:
fitscopy split-00.fits"[col RA;DEC;MAG]" cut-00.fits
fitscopy split-01.fits"[col RA;DEC;MAG]" cut-01.fits
fitscopy split-02.fits"[col RA;DEC;MAG]" cut-02.fits
fitscopy split-03.fits"[col RA;DEC;MAG]" cut-03.fits
fitscopy split-04.fits"[col RA;DEC;MAG]" cut-04.fits
fitscopy split-05.fits"[col RA;DEC;MAG]" cut-05.fits
fitscopy split-06.fits"[col RA;DEC;MAG]" cut-06.fits
fitscopy split-07.fits"[col RA;DEC;MAG]" cut-07.fits
fitscopy split-08.fits"[col RA;DEC;MAG]" cut-08.fits
fitscopy split-09.fits"[col RA;DEC;MAG]" cut-09.fits
fitscopy split-10.fits"[col RA;DEC;MAG]" cut-10.fits
fitscopy split-11.fits"[col RA;DEC;MAG]" cut-11.fits

5) Determine the required scales of index files (refer to the astrometry.net documentation for determining your scales). I am using 1.5°x1.5° FOV images, so I use scales 5, 6 and 7.

6) Edit the build-index.py according to your scale requirements (make other edits if needed). Editing is easy, just change the scale_range variable to whatever you need. After editing and saving, run the script (this will take some time):
# python build-index.py

If everything goes well, you should have 12*[number of different scales] files (in my case I have 36 files, as I have 3 different scales).

7) After building the index files, you need to add an entry to /usr/local/astrometry/etc/astrometry.cfg to use the index files with astrometry.net. Open that file and add:
add_path /tmp/UCAC4
autoindex

8) You can delete all files from the /tmp/UCAC4 folder EXCEPT those beginning with index-ucac4*

9) Enjoy using your UCAC4 index files!

OPTIONAL - TEST IMAGE
1) I have provided a test image (by La Sagra Sky Survey) which will work for scales 5 to 7 and declination range from +24° to +20°. Copy the centu1.jpg image to the directory of your choice and run:
# solve-field centu1.jpg --overwrite --downsample 2 --tweak-order 4

The solved image should have a center in (RA H:M:S, Dec D:M:S) = (07:38:20.142, +22:18:57.895). Congratulations, you made it!