Setup Astrometry.net and usage tips

Astrometry.net is easy to use on Linux, macOS, and Windows. Windows uses Windows Subsytem for Linux for Astrometry.net. To get star index files, use downloadIndex.py.

Download/install the pre-compiled binary code:

  • Linux / Windows Subsystem for Linux: apt install astrometry.net
  • macOS Homebrew

The major steps in achieving a useful WCS starfield polynomial fit are:

  1. source extraction (identifying star position in image frame)

  2. quad asterism hashing, including tolerance for star position wiggling due to noise.

  3. Match hash to star catalog, at least 3 choices are available:

  4. Bayesian decision process, find extremely high probability solution or reject.

Astrometry.new tips and techniques

Optional compile: normally not necessary.

Prereqs:

apt install libcairo2-dev libnetpbm10-dev netpbm libpng12-dev libjpeg-dev zlib1g-dev swig libcfitsio-dev
curl -O https://astrometry.net/downloads/astrometry.net-latest.tar.gz

tar xf astrometry.net-*.gz

cd astrometry.net-*

make
make py
make extra

make install INSTALL_DIR=~/astrometry.net

Add to ~/.profile

export PATH="$PATH:$HOME/astrometry.net/bin"

do not use ~ to avoid error:

cannot find executable astrometry-engine

Uncomment inparallel in ~/astrometry.net/etc/astrometry.cfg (or /etc/astrometry.cfg)

Copy the star index files with downloadIndex.py

python downloadIndex.py

If it can’t find the index file, be sure ~/astrometry.net/etc/astrometry.cfg contains:

add_path /home/username/astrometry/data

~ or $HOME will NOT work!

Reference paper

Program giving azimuth/elevation for each pixel of sky image

Alternative: online astrometry.net image scaling