@BeginModule
@NewPage
@Name      = Gradsdes
@Title     = GrADS data descriptor file
@Section   = Miscellaneous
@Arguments = ifile
@Operators = gradsdes1 gradsdes2

@BeginDescription
Creates a GrADS data descriptor file. Supported file formats are GRIB,
SERVICE, EXTRA and IEG. For GRIB files the GrADS map file is also 
generated. For SERVICE and EXTRA files the grid must be specified with
the CDO option '-g <grid>'. This module takes @file{ifile} in order to create 
filenames for the descriptor (@file{ifile.ctl}) and the map (@file{ifile.gmp}) file.
"gradsdes" is an alias for @oper{gradsdes2}.
@EndDescription
@EndModule


@BeginOperator_gradsdes1
@Title     = GrADS data descriptor file (version 1 GRIB map)

@BeginDescription
Creates a GrADS data descriptor file. Generated a machine
specific version 1 GrADS map file for GRIB datasets.
@EndDescription
@EndOperator

@BeginOperator_gradsdes2
@Title     = GrADS data descriptor file (version 2 GRIB map)

@BeginDescription
Creates a GrADS data descriptor file. Generated a machine 
independent version 2 GrADS map file for GRIB datasets.
This map file can be used only with GrADS version 1.8 or newer. 
@EndDescription
@EndOperator


@BeginExample
To create a GrADS data descriptor file from a GRIB dataset use:
@BeginVerbatim
   cdo gradsdes2 ifile.grb
@EndVerbatim
This will create a descriptor file with the name @file{ifile.ctl}
and the map file @file{ifile.gmp}.

Assumed the input GRIB dataset has 3 variables over 12 time steps on a T21 grid.
The contents of the resulting GrADS data description file is approximately:
@BeginListing
   DSET  ^ifile.grb
   DTYPE  GRIB
   INDEX  ^ifile.gmp
   XDEF 64 LINEAR 0.000000 5.625000
   YDEF 32 LEVELS -85.761 -80.269 -74.745 -69.213 -63.679 -58.143
                  -52.607 -47.070 -41.532 -35.995 -30.458 -24.920
                  -19.382 -13.844  -8.307  -2.769   2.769   8.307
                   13.844  19.382  24.920  30.458  35.995  41.532
                   47.070  52.607  58.143  63.679  69.213  74.745
                   80.269  85.761
   ZDEF 4 LEVELS 925 850 500 200
   TDEF 12 LINEAR 12:00Z1jan1987 1mo
   TITLE  ifile.grb  T21 grid
   OPTIONS yrev
   UNDEF  -9e+33
   VARS  3
   geosp    0  129,1,0  surface geopotential (orography)  [m^2/s^2]
   t        4  130,99,0  temperature  [K]
   tslm1    0  139,1,0  surface temperature of land  [K]
   ENDVARS
@EndListing
@EndExample
