Ferret accepts input data from both ASCII and binary files and recognizes two standardized, self-describing data formats‚ÄîNetCDF, and TMAP. Network Common Data Format (NetCDF) is the suggested method of data storage.
SET DATA_SET or just SET DATA specifies a data set for access. ASCII and binary files can be read using SET DATA/EZ (also known as "FILE"). To unambiguously specify the format of a data set, include the extension .cdf or .des in its name, or use the qualifier /FORMAT=CDF.
To examine what each data set consists of (variables, grids, etc.) after specifying them with SET DATA, use SHOW DATA. This command displays the variables in the data set and over what geographical and time ranges they are defined.
Here is an example of Ferret's output:
yes? SET DATA coads_climatology
yes? SHOW DATA
currently SET data sets:
1> /home/porter/tmap/ferret/linux/fer_dsets/data/coads_climatology.cdf (default)
name title I J K L
SST SEA SURFACE TEMPERATURE 1:180 1:90 ... 1:12
AIRT AIR TEMPERATURE 1:180 1:90 ... 1:12
SPEH SPECIFIC HUMIDITY 1:180 1:90 ... 1:12
WSPD WIND SPEED 1:180 1:90 ... 1:12
UWND ZONAL WIND 1:180 1:90 ... 1:12
VWND MERIDIONAL WIND 1:180 1:90 ... 1:12
SLP SEA LEVEL PRESSURE 1:180 1:90 ... 1:12
If multiple data sets have been requested in a single Ferret session, the last requested will be the default data set. To specify other data sets, use the name of the data set or the number of the set as given by the SHOW DATA statement. For example:
yes? LIST/D=2 temp
will list the data for the variable "temp" in data set number 2 as displayed by SHOW DATA/BRIEF, while
yes? LIST temp[D=levitus_climatology] - temp[D=coads_climatology]
will list the differences between the variable "temp" in data set "levitus_climatology" and data set "coads_climatology."
Once a data set has been opened, you can find the data set name via the RETURN keyword :
yes? say `var,RETURN=dset`
yes? say `var,RETURN=dsetnum`
If a filename begins with a number, Ferret does not recoginze it, but the file may be specified using its unix pathname, e.g.
yes? use "./123"
yes? file/var=a "./45N_180W.dat"