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Vis > visualization > 2d > grads > GFDL Visualization Guide: 2-D Packages

GFDL Visualization Guide: 2-D Packages

GrADS

DESCRIPTION :
The Grid Analysis and Display System (GrADS) is a command- line tool for rapidly accessing, manipulating, and displaying data on a variety of computer platforms. A scripting language, (which supports flow control, defined variables, and access to GrADS command output) is convenient for batch applications. Gridded (or station) data is located within a 4-Dimensional space (usually longitude, latitude, level, and time) through a data description file. GrADS suports the UNIX byte-stream and GRIB data formats, and ingestion of NetCDF data is available in version 1.8. Data may be displayed using a variety of graphical output techniques, including contours, shading, vectors, scatter plots and geography. Freud or VCS can also be used to plot GraDS-compatible data.Widgets (buttons and pull down menus) may be drawn that allow a "point and click" GUI between the Grads user and the  GrADS scripting language. Users may write their own GrADS functions, e.g., grid interpolation functions, in the computer language of their choice, to generate an expression, which can be accessed via the GrADS display command.
PLUSES :
  • rapid, interactive access, manipulation and display of 1-D or 2-D sections
  • animation of 2-D plots
  • plots are very customizable
  • mathematical manipulation / user function capability
  • reads netCDF data and GRIB data
  • DODS enabled
  • reads and plots station data
  • has the capbility for users to implement their own GUI
  • available on all GFDL platforms (linux i86, irix, linux ia64)
MINUSES :
  • one-of-a-kind native GrADS data format is supported by a very limited number of packages, (although the netCDF data format is supported by many packages)
  • GrADS handles only one horizontal grid (i.e., no staggered grids), and one
    vertical grid per file, even if the input data is written as a netCDF file
  • GrADS lacks a 3-D visualization capability
HOW TO INVOKE :
  • To access the latest 1.8 system version of GrADS, which is capable of handling netCDF data, set three environment variables and augment your path.
    Use the following in your ~/.cshrc file: 
    if ( `uname` == IRIX64 ) then
    # ANCs
    setenv GADDIR /usr/local/grads/dat
    setenv GASCRP /usr/local/grads/lib.gs
    setenv GAUDFT /usr/local/grads/udf/udft
    set path = ( /usr/local/grads /usr/local/grads/bin)
else if ( `uname -m` == ia64 ) then 
    # ICs
    set path = ( /usr/local/grads/bin)
    # if you use the 'regrid2' function, use all of the following
    module load ifort.9.0.024  
    setenv GAUDFT /usr/local/grads/udft
    unsetenv F_UFMTENDIAN
endif
  • Startup GrADS by entering :
    • grads
  • To open a GrADS or GRIB file, enter :
    • open <file name>
  • To open a netCDF file, (using a netCDF-capable version of GrADS), enter :
    • sdfopen <file.nc>
  • To quit a GrADS session, enter:
    • quit
    HINTS :
  • Write your input data files in 32 bit ieee byte-stream format, or GRIB format, and create a "description file" (see User's Guide, below); or write your data in the self-documenting netCDF file format.
  • A user defined interpolation function 'regrid2' must be employed to plot the difference of a variable "var" from two different data sets, which do NOT reside on the same grid.
  • The byte swapping option must be included in description files, when running GrADS on your LINUX work station and excluded when running GrADS on UNIX platforms such as the HPCS ANC1 or ANC2, due to the Endian-ness problem.
  • Similarly, view a GrADS metafile and/or transform it into another file format such as postscript, in an AC  window (a work station window), if the metafiles were previously created using the UNIX-based (LINUX-based) GrADS executable.

    •  
    INFO / DOCUMENTATION :
  • To view on-line or to download a hard copy - GrADS Documentation . Select from several options, including The Users Guide, Tutorial, Index, and Downloading hard copy documentation.
  • For more general information about GrADS - GrADS Home Page . Select from several options, including Overview, What's New, Downloading Software, Documentation, etc.

    •  
  • GUIDE to GrADS Documentation at GFDL - README
  • For additional info, GFDL/AOS users should contact Tony Gordon (Rm. 325, ext. 6544, e-mail: Tony.Gordon@noaa.gov)
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    last modified: August 12 2005.