OAGRID creates a GEMPAK grid file which can be used in a Barnes
objective analysis program.

INPUT PARAMETERS
 
    GDFILE    *Grid file
    DELTAN    *Station spacing
    DELTAX    *X spacing
    DELTAY    *Y spacing
    GRDAREA   *Area covered by grid
    EXTEND    *Points to extend grid
    DTAAREA   *Data area for OA
    SOURCE    *Data source (SN or SF)
    SNFILE    *Sounding data file
    SFFILE    *Surface data file
    SNPARM    *Sounding parameter list
    SFPARM    *Surface parameter list
    DATTIM    *Date/time
    LEVELS    *Vertical levels
    MAXGRD    *Maximum number of grids
 
 

PROGRAM DESCRIPTION
 
    This program allows the user to create a GEMPAK grid file
    which contains the information required to perform a Barnes
    objective analysis.

    The output grids will be evenly spaced latitude/longitude
    (CED) grids.  Three areas used by the objective analysis
    programs are defined in this program.  GRDAREA defines a
    region for the output grid.  The upper right corner
    specified will be moved toward the lower left in order
    to align it on a grid point.

    The second area, defined by EXTEND, is used to extend the
    grid area outward by some number of grid points.  This area
    is used as a first-pass grid area in the objective analysis.
    The default EXTEND values are 2,2,2,2.

    DTAAREA defines the area over which station data will be
    input to the analysis.  Only data within the EXTEND area are
    used for the second pass.  If a value for DTAAREA is not
    specified, the EXTEND area will be used.

    If values for the station spacing and grid spacings, DELTAN,
    DELTAX, and DELTAY, are all specified by the user, they are
    stored in the grid file for use by the analysis programs.  If
    any of these numbers is 0, a suggested station spacing is
    computed using the station data from the file specified.  This
    station spacing will be used to compute values for DELTAX and
    DELTAY.  The computed station spacing is the average of the
    average minimum station spacing and the uniform station
    spacing.  These station spacing values are computed using the
    stations reporting data for the first DATTIM.  The average
    minimum station spacing is the average of the distances from
    each station to its closest station.  The uniform spacing is
    the spacing that would be found between stations if they were
    evenly spaced over the data area.

    GDCFIL can also be used to create grid files.  OAGRID creates
    only CED grids, but values for the grid spacing and station
    spacing are estimated from the input surface or upper air file.
    GDCFIL creates grid files for grids in any projection, but
    the grid spacing and station spacing must be input directly.


EXAMPLES
 
    1.  Create a grid file called TEST.GRD.  Use the surface
        temperature data at the latest time from stations in the
        surface file SURFDAT to compute the station spacing.  The
        grid area is WV; use defaults for the remaining parameters.
        Create a file which can contain up to 100 grids.

        GDFILE   =  test.grd
        DELTAN   =  0.
        DELTAX   =  0.
        DELTAY   =  0.
        GRDAREA  =  wv
        EXTEND   =  2;2;2;2
        DTAAREA  =
        SOURCE   =  sf
        SFFILE   =  surfdat
        SFPARM   =  tmpf
        DATTIM   =  last
        LEVELS   =  0
        MAXGRD   =  100

    2.  Create a grid file called GRID.GRD with a station spacing
        of 5, x spacing of 3 and y spacing of 4.  The grid area
        is over PA; the extended grid area should include 1 grid
        point in each direction; the data area is PA-.

        GDFILE   =  grid.grd
        DELTAN   =  5.
        DELTAX   =  3.
        DELTAY   =  4.
        GRDAREA  =  pa
        EXTEND   =  1;1;1;1
        DTAAREA  =  pa-


ERROR MESSAGES
 
    [OAGRID  +1]    WARNING : This grid is too large for GEMPAK programs.
    [OAGRID  -1]    Fatal error initializing TAE.
    [OAGRID  -2]    Fatal error reading TAE parameters.
    [OAGRID  -3]    ... is invalid for GRDAREA.
    [OAGRID  -4]    ... is invalid for DTAAREA.
    [OAGRID  -5]    No data file name specified.
    [OAGRID  -6]    Parameter input is invalid.
    [OAGRID  -7]    Parameter ... cannot be calculated.
    [OAGRID  -8]    Invalid value for DELTAX or DELTAY.
    [OAGRID  -9]    Too few stations to calculate DELTAN.
    [OAGRID -10]    Source must be set to SN or SF.
    [OAGRID -11]    Station data file is invalid.
    [OAGRID -12]    Invalid time requested.
    [OAGRID -13]    Invalid level requested.