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| Part I: Introduction to Reducing the HST Data | |||||
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3.1 Alternative Means of Accessing HST Data
There is much software available to access HST data. This section will mention a few of the more popular alternatives to IRAF.
3.1.1 Interactive Data Language (IDL)
IDL is very popular in the astronomical community. In short it is an array-based, interactive programming language that is strong in numerical analysis and visualization tools. It is typically much easier to develop new analysis and visualization applications and utilities in IDL than in Fortran or C. As a result many astronomers use it for doing analysis of HST data. It is moderately expensive, however, and can be obtained from Research Systems Inc. (
www.rsinc.com/idl/). Libraries for reading HST data are part of the freely available ASTRON library (idlastro.gsfc.nasa.gov) which also has links to other astronomy IDL libraries.3.1.2 Python
Python is rapidly becoming a popular language for astronomical data reduction applications. It is a freely available, general-purpose, dynamically-typed interactive language that provides modules for scientific programming. These include:
- numarray: provides IDL-style array manipulation facilities
- PyFITS: ability to read and write FITS files to and from arrays
- matplotlib: plotting and image display package
- numdisplay: package to display arrays to saoimage, ds9 and ximtool
- PyRAF: package to run IRAF tasks from Python
Python is a very powerful language that is well suited to writing programs to solve many needs beside scientific analysis. It is generally much more productive than Fortran, C, or Java. Tools are available to read (but currently not write) GEIS files. PyRAF allows easy use of IRAF tasks with code written in Python.
STScI is developing most of its new calibration and data analysis software in Python. More information on the use of Python to analyze HST data can be obtained from:
http://www.stsci.edu/resources/software_hardware/pyraf
http://www.stsci.edu/resources/software_hardware/numarray
http://www.stsci.edu/resources/software_hardware/pyfits3.1.3 Fortran and C
For those that wish to write their own Fortran or C applications, we recommend use of the FITSIO library for reading FITS files (
http://heasarc.gsfc.nasa.gov/docs/software/fitsio/fitsio.html; note that the C library is called CFITSIO).This library does not support the GEIS format directly so users will need to use the waiver FITS form obtained from the archive and manually extract the needed information.
3.1.4 Java
The most widely used FITS libraries for Java are the Java FITS Utilities (
http://heasarc.gsfc.nasa.gov/docs/heasarc/fits/java/v0.9/) and the Java FITS Class Library (http://www.eso.org/~pgrosbol/fits_java/jfits.html). Like FITSIO, neither can read GEIS files, however; one must read the waiver FITS file of these data sets.3.1.5 PyRAF
PyRAF is a new command language for IRAF that is based on Python. It has a number of advantages over the IRAF CL. Most importantly, with few exceptions, it allows use of exactly the same syntax that the IRAF CL accepts. Some of the advantages that it provides are:
- true command line recall (with arrow key editing)
- command and filename completion
- GUI-based graphics windows, previous plot recall, multiple graphics windows
- GUI epar editor with display of help in separate window
- IDL-like capabilities
- true error handling for scripts (shows which line the script fails at when errors occur)
- can script IRAF tasks in Python language
- exception handling capability
Since PyRAF is so highly compatible with the IRAF CL, virtually all of the examples shown in this handbook will work the same for PyRAF. Minor differences include the user prompt and the graphics windows appearance.
More information on PyRAF can be found at:
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Space Telescope Science Institute http://www.stsci.edu Voice: (410) 338-1082 help@stsci.edu |