Setup Astrometry.net and usage tips
Astrometry.net is easy to use on Linux and Windows. Windows uses Windows Subsytem for Linux for Astrometry.net.
Install
After install, if you need the star index files, use: downloadIndex.py
Linux / Windows Subsystem for Linux
Download/install the pre-compiled binary code
apt install astrometry.net
Install the star map data necessary to solve images.
apt install astrometry-data-2mass-08-19 astrometry-data-tycho2-10-19
MacOS
Using Homebrew:
brew install astrometry-net
Usage
The major steps in achieving a useful WCS starfield polynomial fit are:
source extraction (identifying star position in image frame)
quad asterism hashing, including tolerance for star position wiggling due to noise.
Match hash to star catalog, at least 3 choices are available:
Bayesian decision process, find extremely high probability solution or reject.
We have written a separate article on Astrometry.new tips and techniques
Notes
[Optional] compile
This is normally not necessary, unless you want to customize/optimize.
Prereqs:
apt install libcairo2-dev libnetpbm10-dev netpbm libpng12-dev libjpeg-dev zlib1g-dev swig libcfitsio-dev
Install: If you have Anaconda/Miniconda Python as your default, Astrometry.net will use them (or whatever your default Python is). Back to at least Astrometry.net 0.70, Astrometry.net is Python 3 compatible.
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 ~/.bashrc
export PATH="$PATH:$HOME/astrometry.net/bin"
do not use ~
or you’ll get 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!
Related:
Program giving azimuth/elevation for each pixel of your sky image
Alternative: online astrometry.net image scaling