Grid Analysis and Display SystemGrid Analysis and Display System
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The Grid Analysis and Display System (GrADS) is an interactive desktop tool that is currently in use worldwide for the analysis and display of earth science data. GrADS is implemented on all commonly available UNIX workstations and DOS based PCs, and is freely distributed over the Internet via
anonymous ftp. GrADS provides an integrated environment for access, manipulation, and display of earth science data.GrADS implements a 4-Dimensional data model, where the dimensions are usually latitude, longitude, level, and time. Each data set is located within this 4-Dimensional space by use of a data description file. Both gridded and station data may be described. Gridded data may be non-linearly spaced; Gaussian grids and variable resolution ocean model grids are directly supported. The internal data representation in a file may be either binary or GRIB.
Since each data set is located within the 4-D data space, intercomparison of disparate data sets is greatly facilitated. Operations may be performed between data on different grids, or between gridded and observational data. Data from different data sets may be graphically overlaid, with correct spatial and time registration.
The user accesses data from the perspective of the 4-D data model. A dimension environment is described by the user as a desired subset of the 4-D space. Data is accessed, manipulated, and displayed within this subset.
Operations may be performed on the data directly, and interactively, by entering FORTRAN-like expressions at the command line. A rich set of built-in functions are provided. In addition, users may add their own functions as external routines written in any language. The expression syntax allows complex operations that range over very large amounts of data to be performed with simple expressions.
Once the data have been accessed and manipulated, they may be displayed using a variety of graphical output techniques, including line, bar, and scatter plots, as well as contour, shaded contour, streamline, wind vector, grid box, shaded grid box, and station model plots. Graphics may also be output in PostScript format for printing on monochrome or color PostScript printers. The user has wide control over all aspects of graphics output, or may choose to use the geophysically intuitive defaults.
A programmable interface is provided in the form of an interpreted scripting language. A script may display widgets as well as graphics, and take actions based on user point-and-clicks. Quite sophisticated data graphical interfaces can, and have, been built. The scripting language can also be used to automate complex multi-step calculations or displays. GrADS can be run in a batch mode, and the scripting language facilitates using GrADS to do long overnight batch jobs.
You may address questions via email to Brian Doty: doty@cola.iges.org. However, please send any questions about GrADS to the listserver first, before sending email directly to Mr. Doty.
The Grid Anlysis and Display System (GrADS) is distributed free
of charge. See file COPYRIGHT in the distribution materials for
more information on the GrADS distribution policy.
The anonymous ftp distribution on
grads.iges.org contains the current production UNIX version in the home directory, the current test version in the beta subdirectory, and the production PC version in the pc subdirectory. Each directory contains aREADME file.
There are other FTP sites which make the GrADS executables available:
To obtain the PC version, connect to directory
pc,
and transfer all the files there to an empty directory
on your PC. Be sure to do the file transfer in binary mode.
Then look at the readme.txt file for information specific to the
PC version.
Within the home directory on the anonymous ftp (the directory you are in when you first connect), you will find the current production version for UNIX workstations, which is still version 1.4. Version 1.5 is in the beta subdirectory, and is at production level except for a lack of updated documentation, which is in preparation. We are anticipating the release of a production version 1.6 in the 4Q 1995.
The UNIX version is distributed as several seperate tar files. The first file contains the binary executables for GrADS for a particular vendor's hardware and software:
grads (main program)
stnmap (station map data set mapper)
gxps (monochrome postscript translator)
gxpsc (color postscript translator)
gxpscw (color postscript, white background)
gribmap (index a GRIB data set)
gribscan (scan a GRIB data set)
gxtran (display metafile on screen)
/usr/local/bin
/usr/local/lib/grads
data.tar)
are in /usr/local/lib/grads, or in the current directory.
To override this default, set the environment variable GADDIR:
setenv GADDIR dirname
If you set the directory name to a period, the current directory is assumed.
To obtain the files, ftp to grads.iges.org (IP 192.239.84.50), log in, and get them. Be sure you use binary mode:
ftp> set binary
To untar the files, go to the directory you want them in, and:
tar -xvf sgi.tar
tar -xvf data.tar
tar -xvf doc.tar
The two files take about 2MB of disk space, depending on machine archetecture (64 bit executables are larger).
The documentation is in:
cbar.gs can be run from the command line by entering
run cbar.gs
It will draw a color bar for a shaded contour plot. It is intended to be run after a shaded plot has already been displayed.
Another sample script is xyplot.gs. A sample xyplot data file that
goes with the script is called xyplot.dat.
Two newer sample scripts are:
wxsym.gs Draws all the wx symbols (see comments in the
script)
cmap.gs Allows user to interactively create color maps
(see comments in the script)
Note: If you are running on a DECstation and wish to run the example,
you will need to first edit the data descriptor file (model.ctl)
and remove the BYTESWAPPED record.
To subscribe, send mail to that address containing the following line:
subscribe gradsusr #####
where ##### is your name.
An online archive for the listserver is maintained at:
