The Grid Analysis and Display System (GrADS) is a free interactive desktop tool that is currently in use worldwide for the analysis and display of earth science data. GrADS provides an integrated environment for access, manipulation, and display of earth science data. GrADS was developed by Brian Doty at the Institute of Global Environment and Society, Center for Ocean-Land-Atmosphere. Arlindo da Silva, at NASA, Goddard Space Flight Center, Data Assimilation Office, has enhanced GrADS enabling it to operate under Windows 95/NT and giving it Athena widget capabilities. He has also made improvements to the MSDOS version of Grads.

Outline

Graphic User Interface

Tips on using the GrADS Interface

Setting GrADS up

Setup for a Unix operating system

Setup for the Windows operating system

GrADS for MSDOS

Starting GrADS

Decompression software

Versions of GrADS available on the CD-ROM

GrADS sites of interest on the World Wide Web

After reading this section go to Setting GrADS up to find out how to run GrADS with the GUI interface.

NOTE: Some data sets (DAO, ISCCP_D2 and TOVS) only have a single date or year, accessible through the GrADS Interface. The rest of the data is compressed.

The selections for the interface are divided into five groups indicated by colors.

Green Selections

• The File pull down menu gives access to the following commands :

  Open ; used to open GrADS command (.ctl) files, by moving through the CD directory structure

  View Text Files ; used to open ASCII files

  Exec ; used to execute GrADS batch files

  Run ; used to run GrADS script files

  Reinit ; used reinitialize GrADS

  Exit ; used exit (quit) GrADS

• The Option pull down menu gives access to the following graphic display commands :

  Continental Boundaries on/of ; turns continental boundaries on or off

  Draw Title ; produces a title for the display

  Color Bar ; produces color bar (scaled to data values) for the display

  Shaded ; produces color shaded (smoothing) plot

  contour ; produces contour plot

  Grid Fill ; produces color (no smoothing) plot

  Grid Values ; produces grid boxes with values

  Vector ; produces vector wind arrows

  Line Plot ; produces line graph (e.g., latitude band)

  Bar Chart ; produces bar chart (e.g., latitude band)

  Note: After selecting one of the above options, you will need to re-display (use "Display" button) current selection before seeing results.

• The Dim pull down menu gives access to the following dimension selection commands :

  Latitude ; select latitude region (e.g., -20 20, form : south to north)

  Longitude ; select longitude region (e.g., -20 20, form : west to east)

  Time ; select date (e.g., FEB1986 ; this will not work for datasets which are compressed and only have one date to select, i.g., dao)

  x ; select x dimension (e.g., 100 200)

  y ; select y dimension (e.g., 90 120)

  z ; select z dimension (e.g., 5 ; only for multi-level files, like DAO upper air products)

  t ; select t dimension (e.g., 20 ; this will not work for datasets which are compressed and only have one date to select, i.g., dao)

  Note: After selecting one of the above options, you will need to re-display (use "Display" button) current selection before seeing results.

Red Selections

• The ga> button gives access to the GrADS command window
• The Help button tells you were to find help documentation

Blue Selections

• These are pull down menus that give direct access to displaying data parameters. They have been organized based on data source as well as parameter involved.

Gold Selections

• The Fresh button redisplays the current display
• The Var button gives access to the "Select a Variable" window
• The << button moves back one date and displays
• The Display button displays the current selections
• The >> button moves forward one date and displays

Grey Selections

• The Hold button retains the previous display when displaying new selection
• The Clear button clears the current display but retains the current selections
• The Reinit button returns GrADS to it's initial state, reseting the events buffer and graphics, closing all open files and releasing all defined objects (you will use this button a lot)
• The Quit button quits or exits from GrADS

Tips on using the GrADS Interface

• When displaying a new parameter, use the reinit button before displaying the data. This will reinitialize GrADS. If you do not do this you may get the error "Entire Grid Undefined". This would happen because the parameters have different initial time steps.
• After using the reinit button the display will be set back to contour, which is the default display for GrADS. The display for the interface is initially set to shaded. If you want the display to be shaded, after using the reinit button, you will have to select "Shaded" from the "Options" menu.
• We have specified the fill value for each parameter in it's control (.ctl) file. This improves the display of the image, because the fill value is not included in the scaling of the color for the display. Some of the CIDC datasets (see individual dataset documentation) use more than one fill value. When displaying such data, the color will be scaled between the second fill value and the maximum data value. This will not look good. To improve the display use the maskout function. This can be done by issuing the following expression at the "Select a Variable" window, which is accessible from the "Var" button.

The value "0.0" is at the lower bound of the NDVI parameters range. For other parameters, use the lower bounds of their range.

For more information on how to use GrADS, see the GrADS manual.

Setting GrADS up

Before starting GrADS you will need to set the environment variables. The Macintosh version of GrADS does not support environment variables, so you can not do this. For additional Information on using GrADS for the Macintosh click here.

Setup for a Unix operating system

Example for the C shell:

setenv GADDIR /"CDROM"/software/grads/dat
setenv GASCRP /"CDROM"/software/grads/lib
setenv GAGUI /"CDROM"/cdrom.gui

alias grads /"CDROM"/software/grads/"VERSION"/grads

export setenv GADDIR=/"CDROM"/software/grads/dat
export setenv GASCRP=/"CDROM"/software/grads/lib
export setenv GAGUI=/"CDROM"/cdrom.gui

alias grads=/"CDROM"/software/grads/"VERSION"/grads

NOTE: You can also start the GUI directly from the GrADS command line, by issuing the following command; gui cdrom.gui.

Setup for the Windows operating system

One way to set the environment variables under Windows is to create a .bat file, that would reside in the Windows directory on your PC. You can name this file grads.bat or any other name. This file should contain the following information:

set GADDIR="D":\software\grads\dat
set GASCRP="D":\software\grads\lib
set GAGUI="D":\cdrom.gui

"D":\software\grads\win32\grads

Where "D" is your CD-ROM drive. This may vary from one PC to the next.

NOTE: You can also start the GUI directly from the GrADS command line, by issuing the following command; gui cdrom.gui.

GrADS for MSDOS

Starting GrADS

• GrADS manual
• GrADS tutorial
• Using ImageMagick in GrADS
• Introduction to creating Graphical User Interrface in GrADS

Decompression software

software/decompression

GrADS available on this CD-ROM:

• SGI Irix version 5, Version 1.7.Beta.8
• SunOS version 4.1.x, Version 1.7.Beta.8
• Win32, for Windows 95/NT, Version 1.7.Beta.8

Versions of GrADS for other operating systems are available from the FTP sites listed below.

GrADS sites of interest on the World Wide Web:

• GrADS Web Site
• GrADS Information Server
• UCAR GrADS FTP Site
• German GrADS FTP Site
• Getting Started
• GrADS for Win32, (Windows 95/NT)
• GrADS for MSDOS
• GrADS with Athena Widgets

NASA	Goddard	GDAAC	CIDC