IVOA Space-Time-Coordinate (STC) library

 This library handles space-time information within the Virtual
 Observatory (VO) according to the IVOA (International Virtual
 Observatory Alliance) STC recommendation.
 .
 The VO knows two implementations for STC metadata, one in XML
 called STC-X and a linear string implementation called STC-S.
 This library provides support for the generating and parsing of
 STC-S expressions and STC-X documents. Moreover, it contains various
 helper functions for the transformation between Earth coordinate
 systems, for dealing with sky coordinates, for time parsing and time
 conversions, and for the definition and conversion of units in STC.