The PAL library is a partial re-implementation of Pat Wallace's popular SLALIB library written in C using a Gnu GPL license and layered on top of the IAU's SOFA library (or the BSD-licensed ERFA) where appropriate. PAL attempts to stick to the SLA C API where possible although palObs() has a more C-like API than the equivalent slaObs() function. In most cases it is enough to simply change the function prefix of a routine in order to link against PAL rather than SLALIB. Routines calling SOFA use modern nutation and precession models so will return slightly different answers than native SLALIB. PAL functions not available in SOFA were ported from the Fortran version of SLALIB that ships as part of the Starlink software and uses a GPL licence.

See pal.news for release notes.

Building

A simple configure script is provided:

./configure --prefix=/usr/local --without-starlink
make
make install

The tests can be run using make check. Use --prefix to specify an install location. Given the history of the source code as a Starlink library the default will be /star.

--without-starlink forces the configure script to forget about any Starlink configurations. This is the safe option if you run into problems when using a simple --prefix for building outside of Starlink. The configure script will assume Starlink is not being used by looking to see if STARCONF_DEFAULT_PREFIX environment variable is set. You may run into problems if STARCONF_DEFAULT_PREFIX is set but you use --without-starlink.

Requirements

Requires that either the SOFA C library or the ERFA library variant (which has a more permissive license than SOFA) be installed. The configure script will abort if neither SOFA nor ERFA can be found. SOFA can be obtained either from http://www.iausofa.org or from an unofficial github repository (with a configure script) at https://github.com/Starlink/sofa/downloads. ERFA can be downloaded from https://github.com/liberfa/erfa.

Missing Functions

Not all SLALIB functions have been added. New routines are added to PAL as demand arises.

Language Bindings

A Perl binding of PAL is available (https://github.com/timj/perl-Astro-PAL) named Astro::PAL and is available from CPAN at https://metacpan.org/module/Astro::PAL. This is a standalone distribution that comes with its own copies of PAL and SOFA and so can be installed directly from the cpan shell.

A Python binding of PAL is available (https://github.com/Starlink/palpy). This is a standalone distribution that comes with its own copies of PAL and SOFA.

The Starlink AST (http://www.starlink.ac.uk/ast) library now uses PAL and can be built either with a private PAL or with an external PAL.

Documentation

The description paper for PAL is: "_PAL: A Positional Astronomy Library_", Jenness, T. & Berry, D. S., in Astronomical Data Anaysis Software and Systems XXII, Friedel, D. N. (ed), ASP Conf. Ser. 475, p307.