Using Templates

GrADS allows you use a single data descriptor file to aggregate multiple data files and handle them as if they were one individual file. The individual data files must be identical in all dimensions except time and in a format GrADS can read. The time range of each individual file must be indicated it its filename.

First, the DSET entry has a substitution template instead of a filename. See below for a description of all the possible components of the template. Second, the OPTIONS entry contains the template keyword. Third, the TDEF entry describes the time range for the entire set of data files.

Templating works on any GrADS data type for which you can write a descriptor file. If you specify any additional OPTIONS keywords in the data descriptor file, make sure the options apply equally to each file included in the template.

Valid components of the substitution template are as follows:

%x1   1 digit decade
%x3   3 digit decade
%y2   2 digit year
%y4   4 digit year
%m1   1 or 2 digit month
%m2   2 digit month (leading zero if needed)
%mc   3 character month abbreviation
%d1   1 or 2 digit day
%d2   2 digit day (leading zero if needed)
%h1   1 or 2 digit hour
%h2   2 digit hour
%h3   3 digit hour (e.g., 120 or 012)
%f2   2 or 3 digit forecast hour
%f3   3 digit forecast hour
%n2   2 digit minute (leading zero if needed)

When specifying the initial time (e.g., NWP model output from NMC and FNMOC), use these substitutions:

%ix1   initial 1 digit decade
%ix3   initial 3 digit decade
%iy2   initial 2 digit year
%iy4   initial 4 digit year
%im1   initial 1 or 2 digit month
%im2   initial 2 digit month (leading zero if needed)
%imc   initial 3 character month abbreviation
%id1   initial 1 or 2 digit day (leading zero if needed)
%id2   initial 2 digit day
%ih1   initial 1 or 2 digit hour
%ih2   initial 2 digit hour
%ih3   initial 3 digit hour
%in2   initial 2 minute (leading zero if needed)

%ch   substitute string

chsub  t1  t2  string

Examples

1. Here's a set of binary files spanning a single month, where each day's worth of hourly data is contained in individual files:
      1may92.dat
   2may92.dat
   ...
   31may92.dat
   Three records must be modified in the data descriptor file. Note that the TDEF entry reflects the entire month's worth of data:
      DSET ^%d1may92.dat
   OPTIONS template
   TDEF 744 linear 0z1may1992 1hr
   
   
2. If your data set expanded, and there were more files containing hourly data for other months and years:
      1jun92.dat
   2jun92.dat
   ...
   1jan93.dat
   Then you would add a template for month and year in your DSET entry and extend the length of your TDEF:
      DSET ^%d1%mc%y2.dat
   OPTIONS template
   TDEF 6624 linear 0z1may1992 1hr

   
   
3. Suppose you have a set of seven netcdf files, each containing monthly data spanning a decade:
      pr.1880_1889.nc
   pr.1890_1899.nc
   pr.1900_1909.nc
   pr.1910_1919.nc
   pr.1920_1929.nc
   pr.1930_1939.nc
   pr.1940_1949.nc
   Then your descriptor file would include the following entries:
      DSET ^pr.%x30_%x39.nc
   OPTIONS template
   DTYPE netcdf
   TDEF 840 linear jan1880 1mo
   
   
4. Here are two netcdf files, one containing 50 years of monthly data (600 time steps), the other 100 years (1200 time steps):
      pr.1851-1900.nc
   pr.1901-2000.nc
   Your descriptor file should include the following entries:
      DSET ^pr.%ch.nc
   CHSUB   1  600 1851-1900
   CHSUB 601 1800 1901-2000
   OPTIONS template
   DTYPE netcdf
   TDEF 1800 linear jan1851 1mo
   If these two data files were located on different disks, you could write out the relevant descriptor file entries this way instead:
      DSET %ch
   CHSUB   1  600 /disk1/pr.1851-1900.nc
   CHSUB 601 1800 /disk2/pr.1901-2000.nc