David Stern, the founder of Research Systems, Inc. (RSI), began the development of IDL while working with NASA‛s Mars Mariner 7 and 9 data at the Laboratory for Atmospheric and Space Physics at the University of Colorado. In 1981, IDL was rewritten in assembly language and FORTRAN for VAX/VMS. IDL‛s usage has expanded over the last decade into the fields of medical imaging and engineering, among many others. IDL‛s programming style carries over much of this FORTRAN-legacy, and has a familiar feel to many astronomers who learned their trade using FORTRAN.

The spread of IDL-usage amongst astronomers can in part be attributed to the wealth of publicly astronomical libraries. The Goddard Space Flight Center (GSFC) maintains a list of astronomy-related IDL libraries, including the well known Astronomy User‛s Library (hereafter ASTROLIB2). We will use some of these GSFC IDL libraries. We note that while IDL is a licensed-software product, the source code of user-written procedures are typically freely available to the community.

To make the most out of this section as a reader, it is important that many of the data discovery, access, and analysis protocols are understood before reading this chapter. In the next section, we provide an overview of some of the NVO terminology with which the reader should be familiar.

The IDL library discussed here is specifically for use with the Virtual Observatory and is named VOlib. IDL‛s VOlib is available at http://nvo.noao.edu and is included with the software distrubution for this book.