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 surface grid file called hbobsfc.grd.  Use the
	temperature and dewpoint in the surface file hrcbob.sfc to
	compute the station spacing.  The grid area is US; use
	defaults for the remaining parameters.  Create a file which
	can contain up to 200 grids.

	GDFILE	 =  hbobsfc.grd
	DELTAN	 =  0
	DELTAX	 =  0
	DELTAY	 =  0
	GRDAREA	 =  us
	EXTEND	 =  2;2;2;2
	DTAAREA	 =
	SOURCE	 =  sf
	SNFILE	 =  $GEMPAK/data/hrcbob.snd
	SFFILE	 =  $GEMPAK/data/hrcbob.sfc
	SNPARM	 =
	SFPARM	 =  tmpc;dwpc
	DATTIM	 =  last
	LEVELS	 =  850
	MAXGRD	 =  200

     2.	Create a upper-air grid file called hbobsnd.grd.  Use the
	temperature and dewpoint at 500 mb from the upper-air file
	hrcbob.snd to compute the station spacing.  Create a file
	which can contain up to 2000 grids.

	GDFILE	 =  hbobsnd.grd
	DELTAN	 =  0
	DELTAX	 =  0
	DELTAY	 =  0
	GRDAREA	 =  us
	EXTEND	 =  2;2;2;2
	DTAAREA	 =  us
	SOURCE	 =  sn
	SNFILE	 =  $GEMPAK/data/hrcbob.snd
	SFFILE	 =  $GEMPAK/data/hrcbob.sfc
	SNPARM	 =  tmpc;dwpc
	SFPARM	 =  tmpc;dwpc
	DATTIM	 =  last
	LEVELS	 =  500
	MAXGRD	 =  2000

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.