Basic Concept of Operation
grads commands are entered in the terminal window and the response from grads is either graphics in the graphics window or text in the terminal window. The three fundamental grads commands:
openopen or make available to grads a data file with either gridded or station data
ddisplay a GrADS "expression" (e.g., a slice of data)
setmanipulate the "what" "where" and "how" of data display
The GrADS "expression," or what you want to look at, can be as
simple as a variable in the data file that was opened, e.g.,
slp or an arithmetic or GrADS function operation on the data,
d slp/100 or
d mag(u,v) where mag is a GrADS intrinsic
The "where" of data display is called the "dimension environment"
and defines which part, chunk or "hyperslab" of the 5-D
geophysical space (lon,lat,level,time,ens) is displayed. The
dimension environment is manipulated through the set command and
is controlled in either grid coordinates (x,y,z,t,e indices) or world coordinates (
lon, lat, lev, time, ens).
The "what" and "how" of display is also controlled by the
set command and
includes both graphics methods (e.g., contours, streamlines) and
d to a file).
GrADS graphics can be written to a file (i.e.,
enable print filename and
In addition, GrADS includes graphic primitives (e.g., lines and
circles) and basic labelling through the
query command is used to get information from GrADS
as which files are opened and even statistics.