draw line

draw line x1 y1 x2 y2

Draws a line from x1, y1 to x2, y2 using current line drawing attributes. See the set line command.

set lfcols

Color where a<b in white (1) and b>a in red (2).

External Utilities

bufrscan
gribmap
gribscan
grib2scan
gxeps
gxps
gxtran
stnmap

Expressions

Operators are:

+    Addition 
-    Subtraction 
*    Multiplication 
/    Division

exp

exp(expr)

Performs the e**x operation, where expr is x. Works on both gridded and station data.

exec

exec file-name <arg0 arg1...arg9>

file-name      the name of a file containing grads commands

grads | gradsdap    

gradsc | gradsnc | gradshdf | gradsdods   

GrADS is an interactive desktop tool for the analysis and display of earth science data. GrADS is used worldwide andfreely available over the internet.

GrADS implements two data models: a 5-Dimensional gridded data model, and a station data model. In the gridded data model, the dimensions are presumed to be latitude, longitude, level, time, and ensemble. In the station data model, data exist at arbitrary locations in space and time. Four dimensions (longitude, latitude, level, and time) are used as a framework in the station data model to guide which station reports are to be examined. Each data set is placed within a 4- or 5-Dimensional space by the use of a data descriptor 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 format in a file may be binary, GRIB1, GRIB2, BUFR, NetCDF, HDF4-SDS, or HDF5.

The Ensemble Dimension

Ensemble Handling in grads

The EDEF entry in a descriptor file 

How to organize the data

Example #1: Lag Ensembles

Example #2: Retrospective Daily Hindcasts from CFS

Example #3: Ensembles with Different Lengths and Start Times in Binary Format

set lat|lon|lev|time|ens

set lat|lon|lev|time|ens val1 <val2>

This set command sets one dimension of the dimension environment using world coordinates.

q ens

q ens

This command returns information about the ensemble dimension. For each ensemble member, the printout includes the index number, ensemble name, length (number of time steps), start time in date format, time axis index of start time, and grib2 codes, if present.

enable print

This command is obsolete beginning with grads version 2.1. It has been replaced by gxprint.

This command opens the output file fname that will contain the instructions in grads metacode format to create a hardcopy of the graphical display. Any existing contents of fname will be lost. The output file fname is referred to as a grads metafile.

eloop

eloop(expr)

The eloop function is similar to the tloop function. When displaying a grads expression (expr) with the E (Ensemble) dimension varying, the eloop function will evaluate the exprwith each designated ensemble member fixed, then reassemble the grids to obtain a final result that is E-varying. The eloop function is provided as a way to obtain E-varying results from functions or expressions that are unable to operate when E is a varying dimension.

set cthick

This command sets the thickness for the contour lines.

Synatx

set cthick thickness

The thickness arg must be an integer in the range of 1 to 12 (or 256 for version 2.1 and later)

query

The query command allows the user to get information about a variety of aspects of the current grads session. Configuration, plot characteristics, graphics specifics, and file structure are some examples. The use of query pos combined with the coordinate transformations is the basis of many interactive applications with buttons and drop menus. The query command may be shortened to simply q. The syntax is:

query <option>
or
q <option>

set cterp

set cterp on|off

Turns spline smoothing on or off. "Sticks" until reset. Shaded contours are drawn without spline fitting, so to insure an exact match when overlaying contour lines and shaded contours of the same field, specify cterp as off. You can still use the csmooth option, which affects both contour lines and shaded contours.

set cstyle

set cstyle style

Sets the contour linestyle. style options are:

0 - no contours 
1 - solid 
2 - long dash 
3 - short dash 
4 - long dash, short dash 
5 - dotted 
6 - dot dash 
7 - dot dot dash 

set csmooth

set csmooth on|off

If on, the grid is interpolated to a finer grid using cubic interpolation before contouring. "Sticks".

Using grads Station Data

This section describes some of the grads commands and functions that are available for analyzing and displaying station data. Please refer to the companion section About Station Data for information on the structure of station data files, how to create them, and how to instruct grads to interpret them properly.

Here are some quick links for skipping through this section:

• Operating on Station Data
• Plotting Station Models
• Drawing Arbitrary Cross Sections

set coslat

set coslat on|off

Sets scaling of the Latitude dimension to be the cosine of latitude, producing a "crunched" effect near the poles. Will only work for 1-D plots in which Latitude (Y) is the varying dimension. Sticks until reset.

cos

cos(expr)

Takes the cosine of the expr. Values are assumed to be in radians. Works on both gridded and station data.

()tcorr

(tcorr (expr1, expr2, tdim1, tdim2

This function produces a spatial map of temporal correlation coefficients.

expr1   - a valid grads expression that varies in time
expr2   - a valid grads expression that varies in time and may also vary in X and Y
tdim1   - starting time dimension expression 
tdim2   - ending time dimension expression 

()scorr

This function calculates the spatial correlation between two variables over an X-Y domain. It returns a single number. The syntax is:

(scorr(expr1, expr2, xdim1, xdim2, ydim1, ydim2

Components of a grads Data Descriptor File

query

The query command allows the user to get information about a variety of aspects of the current grads session. Configuration, plot characteristics, graphics specifics, and file structure are some examples. The use of query pos combined with the coordinate transformations is the basis of many interactive applications with buttons and drop menus. The query command may be shortened to simply q. The syntax is:

()const

const (expr, value, <-u|-a>)

This is a powerful function that allows the user to change the missing values of a variable, set all the non-missing values of a variable to a constant, or set all possible values of a variable (both valid and missing) to a constant.

expr   a valid grads expression 
value  a constant, either an integer or floating point value 
-u     all missing data are set to value; non-missing data are unchanged
-a     all data are set to value, both missing and non-missing

query

The query command allows the user to get information about a variety of aspects of the current grads session. Configuration, plot characteristics, graphics specifics, and file structure are some examples. The use of query pos combined with the coordinate transformations is the basis of many interactive applications with buttons and drop menus. The query command may be shortened to simply q. The syntax is:

query <option>
or
q <option>

Reading and Writing Compressed Data Sets

Command line editing and history

If the readline library compiles on your system then the default prompt will be ga-> as opposed to ga>. This indicates that command line editing is active. The library defaults toemacs mode but can be set up to run using vi syntax.

Here's a list of the commands which may typically be used:

ctrl-a   go to beginning of line 
ctrl-e   go to end of line 
ctrl-f   go forward one char 
ctrl-b   go backward one char 
ctrl-d   delete the char 
ctrl-p   recall previous line
ctrl-n   recall next line
ctrl-r   reverse search

Controlling Colors in grads

The grads Default colors

	Col#  Description   Sample    R   G   B  



	 0   background  0   0   0 (black by default) 



	 1   foreground  255 255 255 (white by default) 



	 2   red  250  60  60  



	 

()coll2gr

This function creates a grid from a collection of station data. The syntax is:

(<coll2gr(cnum <,num

cnum     collection number
num      number of vertical levels in the output grid (default is 10)

collect

This command provides a way for station data profiles and time series to be saved in memory as a set. The command format is:

collect cnum expr

set cmin

set cmin value

Contours not drawn below this value. Reset by clear or display.

set cmax

set cmax value

Contours not drawn above this value. Reset by clear or display.

set cmark

set cmark marktype

Set the style of the marker for line plots, or for the gxout option 'stnmark'. marktype may be one of the following:

set clskip

set clskip number <spacing>

For example, set clskip 2 would label every other contour.

close

close the last descriptor file number for current file

set clopts

Syntax

set clopts color <thickness <size>>