New GILDAS Release

A new release of GILDAS,
dated FEB2000, is available.

A Major Revision of GILDAS

Following a number of discussions and developments, the GILDAS working group has implemented a number of significant revisions in the GILDAS software. These modifications concern the command interface, SIC, the support of FITS files, and speed improvements in the synthesis imaging package (MAPPING and associated imaging tasks) to allow handling of large images in view of the ALMA project.

SIC syntax

The most important change for the user is a modification of the syntax of SIC commands. This will be annoying for some users in a first step, but has proved to be practical because it offers a much simpler handling of filenames and mathematical expressions. The change concerns command options and case conversion.

• Option delimiter:
  In the previous release, options were recognized as words following a slash (/). The slash did not need to be preceded by a space. This had the disadvantage of preventing to use the slash (/) as a divide operator in mathematical expression. Spaces and slashes were both recognized as word delimiters, and redundant delimiters were ignored.

  In the new release, the space is the only word delimiter. Options are words beginning with a slash. Hence to be recognized as an option identifier, a slash must be preceded by a space. The slash can now be used as the divide operator (although the vertical bar continues to work).

  Example where /NEW is an option:

     LET A 1|COS(PI*0.01)/NEW REAL    ! Old 
     LET A 1/COS(PI*0.01) /NEW REAL   ! New
  

• Case conversion:
  SIC is now case sensitive, with the exception of command names and options, SIC variables, and generally command keywords (unless implemented differently by the application programmer).

  In particular, command procedure names, which are derived from filenames, are case sensitive (if the underlying operating system is case sensitive for filenames). For example @ ToTo and @ TOTO are no longer equivalent.

• Filename handling:
  The previously cumbersome way of preventing case conversion for filenames is obsolete (it consisted in enclosing the filename between quotes, and preceding it with an exclamation mark (!)).

     TYPE "!../DIREC/MyFilename.dat"  ! Old 
     type ../DIREC/MyFilename.dat     ! New
  

  In addition, to improve interoperability between Unix and Windows, the backslash ( $\backslash$) is also recognized as a directory delimiter in filenames.

     TYPE ..\DIREC\Myfilename.dat
     TYPE ../DIREC/MyFilename.dat     ! Same
  

With the above modifications, the SIC syntax is more rigorous and avoids some of the confusing messages which occurred in the previous version. While we acknowledge that this will be slightly frustrating at the beginning for some users (50 % of the users used to type the space before the option delimiter anyhow), it greatly simplifies the handling of filenames.

SIC Command Procedures

Two new facilities have been implemented to simplify the maintenance of the large set of command procedures used as user interfaces for several data reduction packages based on SIC, like the Plateau de Bure imaging tools, or the NIC bolometer software.

First, the procedures have been grouped by type (file extension) in separate sub-directories for CLASS, CLIC, GRAPHIC, GREG, MAPPING, NIC, and ASTRO. The access path to these sub-directories is defined by a SIC logical name called MACRO#DIR:.

Second, new commands have been added to allow a command procedure to create any sub-procedure or data set it may need. The commands

   SIC\BEGIN PROCEDURE ProcedureName
   SIC\BEGIN HELP HelpFileName
   SIC\BEGIN DATA DataFile
and
   SIC\END PROCEDURE ProcedureName
   SIC\END HELP HelpFileName
   SIC\END DATA DataFile

allow to create new procedures, their associated help files, and even (ASCII) data files in a procedure. The corresponding files are located in the directory associated to the SIC logical name GAG_PROC:.

SIC - FITS interface

Two new commands have been implemented to allow reading for any type of FITS file in SIC.

    DEFINE FITS Name FitsFile

will read a FITS format file, and define a SIC structure which will contain in its variables and sub-structures all the content of the FITS file. Simple FITS images are stored in variable Name%DATA. Binary and ASCII table extensions are recognized and stored in suitable variables. FITS keywords are also stored (e.g. Name%KEYWORD).

Standard keywords like NAXIS, NAXISi, CRPIXi, CRVALi, etc...are re-mapped to the SIC variables Name%NDIM NAME%DIM Name%CONVERT to be similar to SIC image headers.

SIC structures are ensembles of SIC variables. The syntax of SIC structures is similar to Fortran-90 (e.g. Name%SubName%SubSubName). Besides the structures automatically defined by the DEFINE FITS command, the commands

   DEFINE STRUCTURE Name
   DEFINE REAL Name%A Name%B

can be used to define new SIC structures.

A special hook has been provided in GreG to easily display FITS images using the DEFINE FITS command. The following procedure will plot a FITS image:

   DEFINE FITS A FitsFile
   LIMITS /RGDATA A
   PLOT
   BOX

Most type of FITS files are supported. However, the UVFITS format is not supported, because it has been declared as obsolescent by the IAU FITS Working Group, and should be replaced by binary tables.

Imaging Improvements

Simulation of ALMA images has required to invest some effort into optimization of the imaging tasks in GILDAS. Based on work by Alain COULAIS (now at IAS) and Francois VIALLEFOND (DEMIRM - Observatoire de Paris), the basic imaging tool, UV_MAP has been considerably speeded up (by factors 4 to more than 20, depending on problem size).

The new UV_MAP tool can process more than 1 Million visibilities and create a 2048 x 2048 image in about 1 minute of elapsed time on a HP-J240 machine. On a Dell Inspiron (a laptop) PII-366 MHz with 256 MBytes of memory, and running Windows-98, the same problem takes 90 seconds. On the HP machine, which had 512 Mbytes of memory, a 4096x4096 image takes 3 minutes. The command UV_STAT which allows to compute beam sizes as function of taper and/or robust weighting parameter, has also been improved.

Several new tasks have been added to allow array simulation. Use the command

    GRAPHIC> @ simulate

to access the simulation package in GRAPHIC.

S. GUILLOTEAU and the GILDAS Working Group