Introduction and Installation¶
astLib provides some tools for research astronomers who use Python. It is divided into several modules:
astCalc (general calculations, e.g. luminosity distance etc.)
astCoords (coordinate conversions etc.)
astImages (clip sections from .fits etc.)
astPlots (provides a flexible image plot class, e.g. plot image with catalogue objects overlaid)
astSED (calculate colours, magnitudes from stellar population models or spectral templates, fit photometric observations using stellar population models etc.)
astStats (statistics, e.g. biweight location/scale estimators etc.)
astWCS (routines for using FITS World Coordinate System information)
The astWCS module is a higher level interface to PyWCSTools, a simple SWIG (http://www.swig.org) wrapping of some of the routines from WCSTools by Jessica Mink (http://tdc-www.harvard.edu/software/wcstools/). It is used by some routines in astCoords, astImages and astPlots.
The goal of astLib was to provide features useful to astronomers that are not included in the scipy (http://scipy.org), numpy (http://numpy.scipy.org) or matplotlib (http://matplotlib.sourceforge.net) modules on which astLib depends. For a far more extensive set of Python astronomy modules, see astropy (http://www.astropy.org/).
Some scripts using astLib can be found in the examples/ folder provided with the source code distribution.
Python (tested on versions 3.6+)
Astropy - http://www.astropy.org (tested on version 3.2.1)
Numpy - http://numpy.scipy.org (tested on version 1.18.1)
SciPy - http://scipy.org (tested on version 1.3.1)
Matplotlib - http://matplotlib.sourceforge.net (tested on version 3.1.1)
From astLib 0.10.0, pyfits is no longer supported, as STScI have depreciated it. If you still require pyfits instead of Astropy, please continue to use astLib 0.9.3.
Python Imaging Library - http://www.pythonware.com/products/pil (tested on version 1.1.7)
Other versions of the software listed above are likely to work.
You can install astLib via pip:
pip install pip
You may also install using the standard
setup.py script, e.g., as root:
sudo python setup.py install
python setup.py install --user
$HOME/.local (on Ubuntu), and in some other default location on Mac.
You can also use the
--prefix option, e.g.,
python setup.py install --prefix=$HOME/local
and then add, e.g.,
$PYTHONPATH (adjust the path according to your Python version number).
Installation on recent versions of macOS¶
Some users have reported that the standard method for installing
astLib does not work on recent versions
of macOS (e.g., Big Sur), due to the default compiler flags. The current workaround for this is to install
CFLAGS="-Wno-error=implicit-function-declaration" python setup.py install
Thanks to Michael Cowley and Stefano Covino for helping to resolve this issue.
To access the routines in the astLib modules, simply:
from astLib import astCalc from astLib import astCoords from astLib import astWCS
The astWCS module currently provides access to what are (I think) the most commonly needed WCS information and functions (such as converting between pixel and WCS coordinates etc.). However, should you wish to access the wrapped WCSTools routines themselves directly:
from PyWCSTools import wcs from PyWCSTools import wcscon
Note that PyWCSTools only includes some functions from wcs.c and wcscon.c at present. For examples of usage, look at the Python code for the astLib.astWCS module. Documentation for the WCSTools routines can be found here: http://tdc-www.harvard.edu/software/wcstools/subroutines/libwcs.wcs.html.
As of version 0.11.x+, by default the
astWCS.WCS class is using the
astropy.wcs module instead of
PyWCSTools (this allows one to benefit from some features of
astropy.wcs without having to re-write
code based on
astWCS.WCS). To use PyWCSTools instead, set
useAstropyWCS = False when creating a
This may no longer apply, but just in case…
Recent versions of matplotlib (on which astLib depends) now use locale information. On systems where the decimal point separator is not ‘.’ (e.g. Germany), the astWCS coordinate conversions routines will give strange results if this is not accounted for. As of version 0.3.0, the astWCS module will detect if this is the case and print a warning message to the console.
The workaround for this issue is to add the following after importing any python modules that expicitly set the locale (such as matplotlib):
import locale locale.setlocale(locale.LC_NUMERIC, 'C')"
Thanks to Markus Demleitner for pointing this out.
Please include details of your operating system, python version, and versions of the python packages required by astLib that you have installed on your machine. For any WCS-related bugs, it would be helpful if you could also include the image header as a text file so that I can reproduce them easily.