SOFA Documentation

The basic documentation for the SOFA collection is terse, consisting of (i) detailed preamble comments in the individual routines and (ii) classified and alphabetic lists of subroutine calls. These manuals (Fortran and ANSI C), which have also been split into various sections, are available with each issue, either the current issue or from the SOFA software archive.

SOFA currently offers the following cookbooks, available in pdf format.

  SOFA Tools for Earth Attitude

SOFA Tools for Earth Attitude deals with the important subset of SOFA routines concerned with the Earth's orientation and rotation. First released on 2007 August 01, this cookbook supplements the basic documentation with descriptive material and cookbook examples on the topics of precession, nutation, polar motion, sidereal time and Earth rotation angle. The examples include methods using both the equinox-based and celestial intermediate origins. Versions of this cookbook are available for Fortran and ANSI C.

  SOFA Time Scale and Calendar Tools

There are two versions of this cookbook, for Fortran 77 and ANSI C respectively. The texts are identical, but the code for the examples is appropriate to the particular language.

This cookbook deals with the seven time scales recognized by SOFA, namely, TAI, UTC, UT1, TT, TCG, TDB and TCB and the related civil calendar and Julian date conversions. In the case of UTC, leap seconds are dealt with correctly.

  SOFA Astrometry Tools

There are two versions of this cookbook, for Fortran 77 and ANSI C respectively. The texts are identical, but the code for the examples is appropriate to the particular language and the files in Fortran and ANSI C are provided for users.

This cookbook looks at a selection of SOFA routines that deal with the chain of astrometric transformations linking (i) star data from a catalogue and (ii) the observed direction of the incoming radiation and describes the main astrometric reference systems used by astronomers.

The document SOFA Astrometry Tools at a Glance provides a two page summary of the routine names and abbreviations for the transformation of star positions between the various reference systems in the cookbook.

  SOFA Vector Matrix Library

There are two versions of this cookbook, for Fortran 77 and ANSI C respectively. The texts are identical, but the code for the examples is appropriate to the particular language.

This document covers the angle/vector/matrix tools that were either implemented in the course of writing the SOFA astronomical library or that were thought to be useful in writing general astronomical applications. These routines operate on ordinary Cartesian vectors (x,y,z) and 3x3 matrices plus a few related to spherical angles.

  SOFA Miscellaneous Topics

Forty SOFA routines are not mentioned in the existing cookbooks; in some cases simply because the routine was developed after the relevant cookbook had been written. To address this deficiency, enhancements have been drafted to two of the existing cookbooks (those on astrometry and Earth attitude) and a new one (on miscellaneous topics) has been written. Topics include ecliptic and galactic coordinates, Hipparcos/FK5 and FK4/FK5 transformations, geodesy and solar-system ephemerides.

There are two versions of this cookbook, for Fortran 77 and ANSI C respectively. The texts are identical, but the code for the examples is appropriate to the particular language.