Astronomical Image Processing System: Difference between revisions

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{{Infobox software

| name = AIPS

| logo = [[File:Logo.aips.png|64px]]

| screenshot =

| developer = [[NRAO]]

| latest_release_version =

| latest_release_date =

| status = Active

| programming language = [[FORTRAN]] and [[C (programming language)|C]]

| operating_system = [[Unix-like]]

| genre = Astronomical Analysis

| license = [[GNU General Public License]]

| website = http://www.aips.nrao.edu/index.shtml

}}

{{Portal|Astronomy}}

{{no footnotes|date=March 2014}}

The '''Astronomical Image Processing System''' (AIPS) is a software package to support the reduction and analysis of data taken with radio telescopes. Developed predominantly for use with the then under-construction [[Very Large Array|VLA]], the generality inherent in its design allowed it to become the standard data-reduction package for most radio interferometers, including [[VLBI]]. Limited single-dish capability is also featured. Although partially replaced by CASA, it continues to evolve and remains widely used.

[[File:Logo.aips.png|thumb|right|The emblem of AIPS]]

The '''Astronomical Image Processing System''' (AIPS) is a package to support the reduction and analysis of data taken with [[Radio telescope|radio telescopes]]. The software was originally developed by [[NRAO]] in the seventies for use with the then under-construction [[Very Large Array|VLA]], but the generality inherent in its design allowed it to become the standard data-reduction package for other [[Interferometry|interferometric]] arrays such as [[MERLIN]], the [[Very Long Baseline Array|VLBA]] and the [[European VLBI Network|EVN]], and can also be used to process data from other arrays. Although primarily a tool for analysing data from interferometers, it also has limited ability to work with single-dish data. The official software used by the upgraded VLA (EVLA) and [[Atacama Large Millimeter Array|ALMA]] is [[AIPS++#AIPS++/CASA|CASA]], but AIPS remains the dominant data-reduction package in use today.

==History==

{{unreferenced|date=October 2014}}

Development of AIPS started at [[NRAO]] in 1978, two years before the VLA became fully operational. Originally written in [[FORTRAN 66]], AIPS has used [[FORTRAN 77]] since 1989. The very first AIPS installation was on a [[MODCOMP]] computer, but the package's portability has led to it being installed on multiple systems and is today mostly used by astronomers running [[Linux]] or [[Mac OS]].

AIPS is what most of us{{who|date=October 2014}} would now describe as “legacy software”, having been originally coded in a truly ancient dialect of [[FORTRAN]] (predating even the venerable FORTRAN IV). AIPS now uses FORTRAN 77, although it has been digested successfully by at least one FORTRAN 90 compiler.

A [[MODCOMP]] computer in [[Charlottesville, Virginia]] was the first system to actually host a working AIPS system, and it quickly spread to a guest UNIX system hosted on an IBM 360 mainframe. From there, it spread in the early 1980s to VAX/VMS systems, often with an attached floating-point systems array processor (this peculiar device was the moral equivalent of the 80387 floating-point accelerators that some old-timers may remember being part and parcel of many 386 systems). In the late 1980s, [[UNIX]] came back into the AIPS universe in a big way, first with the Sun-3 series of Motorola-68020-based systems and then with a series of others, including Cray (Unicos), Convex and Alliant systems.

By the time the 1980s were winding down, the dominance of VMS in the AIPS universe was being seriously questioned. Performance on new upstarts like [[Sun Microsystems|Sun]] was starting to challenge their price/performance ratio, and the first [[SPARCstation|SPARCstations]] totally blew them away. In the early 1990s, AIPS moved to a smorgasbord of UNIX variants: AIX, Stardent (briefly), Ultrix, HP-UX, SGI's Irix and [[Tru64 UNIX#OSF/1|DEC OSF/1]]. A port to an [[IBM 3090]] was attempted, but failed due to accuracy problems with the [[IBM Floating Point Architecture|non-IEEE floating-point format]] thereon. In the middle of this flurry of activity, the port to Linux by Jeff Uphoff was made.

===The Blacksburg Connection===

In the fall of 1993, [[National Radio Astronomy Observatory|NRAO]] got a query from a radio astronomer at [[Virginia Tech]] in [[Blacksburg, Virginia|Blacksburg]], requesting permission for one of his students to copy AIPS to his PC for an attempted port to a new system called [[Linux]]. (At that time, AIPS was still proprietary code, released to non-profit organizations under a rather cumbersome license and user agreement; this changed later.) Polite skepticism was the immediate reaction of most people then in the NRAO AIPS group, but they allowed the experiment to go ahead. Within several weeks Jeff Uphoff had successfully ported the software to Linux and was able to run the “Dirty Dozen Tasks” (DDT) benchmark, even though it took about a day on a 386 compared with an hour on a SPARC processor.

At the same time, the capabilities of AIPS have also greatly expanded. Initial usage was focused on the VLA, but it has gone on to be used to reduce data from practically all radio interferometers, including [[MERLIN]] and the [[GMRT]] and, to a lesser extent, the [[Westerbork Synthesis Radio Telescope|WSRT]] and [[Australia Telescope Compact Array|ATCA]]. The ability to calibrate VLBI data (including [[space VLBI]]) was added in the 1990s, primarily to support operations with the [[Very Long Baseline Array|VLBA]], but in the process becoming the main data-reduction package for the [[European VLBI Network|EVN]] and combined VLBA/EVN observations (Global VLBI). Single-dish support was also added in the 1980s, with particular application to NRAO's [[ARO 12m Radio Telescope|12-m radio telescope]] and the 91-m transit telescope.

===Faster and Faster, and Make it GNU===

Within a few months of the original port, NRAO had Jeff Uphoff on its payroll, and the race was on to improve the performance of AIPS on Intel hardware. In the process, the NRAO Charlottesville Computing Division ended up with many Linux machines performing server duties, and several programmers and scientists volunteered for converted to use on Linux systems.

However, it took the use of the EGCS version of the GNU g77 FORTRAN compiler to push the Intel/Linux platform to the forefront of the Radio Astronomy community. In 1995, using EGCS version 1.0.2, AIPS was successfully built under g77. This improved the AIPSMark (a benchmark, defined as 4000 divided by the elapsed time in seconds to run the DDT on a test dataset; bigger AIPSMarks are better and a Sparc IPX is 1.0) on a Pentium Pro 200 from 3.3 to about 5. With further coaxing via aggressive use of optimization parameters, the resulting AIPSMark went over 6. In this fell swoop, the price/performance curve that was previously occupied by Sun, IBM, DEC and HP was shattered once and for all. By 1998, NRAO was ordering Linux/Intel desktops as the workstation of preference for the scientist in place of [[UltraSPARC]] systems. In 1999, Linux started to edge out the high-performance public workstations such as Alpha and high-end SPARC.

AIPS has now been in use for over 30 years and has even outlived its supposed replacement [[AIPS++]], which was eventually rebranded as CASA. CASA has gone on to be the main data-reduction package for the upgraded VLA (EVLA) and [[Atacama Large Millimeter Array|ALMA]], but AIPS remains able, to a large degree, to process data from these state-of-the-art instruments. Despite its age and limited resources, AIPS remains widely used and under active development. AIPS is free software and is covered by the terms of the [[GNU General Public License]].

During this time, another significant change came about. All this exposure to [[copylefted]] code was taking its toll. As mentioned earlier, AIPS was originally released under a restrictive user agreement that prohibited redistribution and was unpalatable or even unacceptable to some in the astronomical community. Not only that, but the administrative costs associated with it were a burden. Thus, around 2000 the decision was made to shift AIPS over to the [[GNU]] (Free Software Foundation's) [[General Public License|GNU General Public License]] on its next periodic release.

==Description==

Currently, a new version of AIPS is released towards the end of each year and is continually updated until the release of the next version. A newsletter ("AIPSLETTER") is released twice a year with information on the recent developments.

AIPS runs under [[X Windows]] with commands entered interactively using a command-line interpreter called POPS. Although relatively primitive, this gives access to a useful collection of e.g. mathematical functions, logical operators and flow control statements. Commands can also be placed in a text file which makes repeating complicated procedures much more convenient and which can be used to create data-reduction [[Pipeline (computing)|pipelines]]. A more modern alternative is to install ParselTongue, a [[Python (programming language)|Python]]-based interface.

As well as the terminal window from which AIPS is started and commands entered, most AIPS sessions will by default contain two other windows, the AIPS TV and the Message Server. The TV is used to visualise data or images and can, for example, be used to interactively edit data or control the progress of a [[deconvolution]]. The Message Server displays useful information reported by each task. Optionally, basic black and white plots can be displayed using TEKSRV, a [[Tektronix 4010|Tektronix 4012]]-based graphics terminal.

==Usage and design==

In general AIPS uses 8 character long "tasks" that have input parameters, and a source and a destination "disk", reminiscent of 1970's era mainframe programming. The "disks" are stored in a catalog, basically predating any notion of filesystems in their modern sense. When using the data, you first load it onto a disk from an external source, usually a [[FITS]] file, either UVFITS or FITS-IDI. You then perform your tasks on these disks, writing the result to an output disk.

Before any data can be processed by AIPS, they must first be imported into the system's own data areas, usually in [[FITS]] format. The FITS standard was agreed in 1979 and its development is inseparable from that of AIPS. The data can henceforth be processed using a large number (>530) of individual programs, each of which performs a specific task e.g. producing an image from a calibrated data set. Together these allow a user to visualize, edit and calibrate a data set and subsequently make images or fit models. A number of analysis tasks are included (e.g. Gaussian fitting to images or spectra) as well as the possibility to make publication-quality plots.

AIPS uses a primitive command-line interpreter known as POPS.

Extensive help is available to AIPS users, with detailed information on each parameter and task viewable from the command line. There is also a [[user guide]], the AIPS Cookbook, which is built around examples (recipes) of how to run the various tasks. It is available on-line, as well as being packaged with AIPS in [[PDF]] and [[PostScript]] formats. A newsletter (AIPSLetter) is published biannually.

==See also==

*[[AIPS++]], a package designed to be a successor to AIPS

*[[IRAF]], a reduction environment for CCD images

==External linksPrimatology==

Although briefly known as RANCID, the eventual choice of name has led to a preponderance of primate-based humour in and around AIPS. The Cookbook contains "additional recipes", genuine food-based concoctions all featuring bananas as an ingredient e.g. banana curried chicken. The programmers guide is called Going AIPS!, the cover of which features a gorilla clutching a [[Tektronix 4010|Tektronix 4012]] graphics terminal whilst standing upon two [[IBM 3420]] Magnetic Tape Units. Various cover designs of the Cookbook also include images of primates.

* [http://www.aips.nrao.edu/ AIPS homepage]

* [http://www.linuxjournal.com/article/4040 Linux Journal article]

[[Category:Radio astronomy]]