3.1 Reduction Software

Several packages already exist to aid the astronomer in reducing data (e.g., STARLINK, IRAF, IDL etc.) and most can be automated at some level. However most astronomers will not write generic routines, due to the complexity of such a task, and will need to create a new software procedure each time they reduce new data. Indeed most will not write routines at all but will carry out each step of the data reduction by sitting at a terminal and manually initiating each command every time it is to be carried out.

3.1.1 FITSIO

Pence (1992) reported on “FITSIO” a high-level machine independent FORTRAN 77 subroutine interface for reading and writing data files in the FITS format (see section Section 5.2). The library was initially written, by the High Energy Astrophysics Science Archive Research Centre (HEASARC) at NASA, for converting various existing and newly acquired data sets into the FITS format (Pence, 2000). To enable machine independency FITSIO operates byte-swapping routines for computers with a big-endian storage architecture (see Section 5.3.2). The library has been evolving constantly since its introduction. For example in 1993 work was started on allowing FITSIO to read and write compressed format FITS files, this was carried out by attempting to make the compressed FITS files a “legal” FITS format as seen by FITSIO Pence (1993). At the same time the library became much more transparent to the user and easier to use, new routines were also introduced expanding the core facilities. Notably, also reported was a set of C wrapper routines, this allowed the FORTRAN 77 library to be called from a C program, again an important issue for the LT where all control software is to be written in C and Java.

In 1995 important steps were taken in making FITSIO a future option for use on an up-gradable PL. It was decided (i) to continue work on compression read/writing of FITS files (ii) to maintain the FITSIO software to keep pace with any new standards or conventions adopted by the FITS community, (iii) to add error checking routines for FITS input/output, (iv) to allow the accessing of FITS files across computer networks and (vi) to explore the possibility of supporting a world co-ordinate system (see Pence, 1995, and Section 5.5).

3.1.2 The StarLink Collection

StarLink¹ (SL) is an extensive library of astronomical data reduction software. Each package runs from the command line, whilst scripting the software into reduction routines is possible, one of the mission statements of SL is “to provide interactive data reduction and analysis tools” (STARLINK, 2002). The collection works using its own data format, the N-dimensional-data-format (ndf), if data is to be reduced using SL then it must be converted to this format. However recently SL have announced that this format has encountered problems; large standard format data cannot be converted into an ndf (see Giaretta et al., 2001).

3.1.3 SExtractor

SExtractor² (Source-Extractor) is a program that generates a list of objects from an astronomical image. It is oriented towards large scale galaxy-survey data, but will work on star fields (Bertin, 1999) and is a command line operated program which has recently gained a large following in the astronomical community; SExtractor is the best performing package of its kind (Andreon et al., 2000). SExtractor will also perform rudimentary photometry, but again the process is oriented toward galaxy work. Also of note is the intention of the author (Bertin) to convert the code into an open-source software library, which will allow full integration of SExtractor (or parts there of) into new routines.

3.1.4 World Co-ordinate System Tools

The WCSTools³ package, in its current incarnation of accessible routines and programs was announced during the writing of the LT PL (Mink, 1998). WCSTools is a package of programs and a library of utility subroutines for setting and using the world coordinate systems (WCS) in the headers of the most common astronomical image formats, to relate image pixels to sky coordinates.

The current version (V3.0, 2000) also contains many facilities to manipulate standard format data and tools to help PL developers. The software is all written in portable C, which should compile and run on any computer with a C compiler.