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ASCII/Binary Grid File

This type of file is generated by the sfccalc, upcalc, focalc, grbcalc, griblook, grid and grdmath programs for use with other WXP grid display programs such as contour and vector.

FORMAT

The contents of the gridded files are standardized to work with all WXP programs. They contain the following information:

WXPGRID
date
[flag-]info
[src ver model grid ltype level ftime var:units]
proj clat clon dx dy nx ny
grid...

Header Data

The first line of the file is the string:

WXPGRID

which is used to determine file type. The second line of the data file is a character string describing the valid time and origin of the image (maximum 50 characters). Examples:

12Z 14 JUN 98
WXP analysis for 12Z 14 JUN 98
24 hour NGM valid 00Z 2 JUN 98

The third line contains a character string describing the contents of the image (maximum 50 characters). Examples:

Integrated Cloud Coverage (%)
IR Temperature (C)

The third line may contain a flag which describes file format.  The flag can be:

  • 2 -- grid file with extended header and ASCII gridpoint data
  • 3 -- grid file with extended header and binary gridpoint data.

Extended Header Data

The grid description line contains grid description variables in the following format:

src ver model grid ltype level ftime var:units

Where:

  • src -- Grid source,
  • ver -- Grid version,
  • model -- Grid model,
  • grid -- Grid type,
  • ltype -- Level type,
  • level -- Vertical level (units depend on ttt),
  • ftime -- Forecast time in hours,
  • var -- Variable type
  • units -- Variable's units (optional)

Example: 7 1 39 50 1 0 24 350

The values of these variables are described in WXP Product Description Appendix.

Domain Header Data

The fourth line contains image size and location in the following format:

proj[:param...] clat clon dx dy nx ny

Where:

  • proj -- The projection:
    LL -- lat-lon,
    PS -- polar stereographic,
    ME -- mercator,
    LC -- lambert conformal. (see plot_domain section of Users Guide for more projections)
  • param -- The projection parameters (see plot_domain section of Users Guide).
  • clat -- The central latitude (N) of the grid.
  • clon -- The central longitude (E) of the grid.
  • dx -- The X coordinate grid spacing based on projection.
  • dy -- The Y coordinate grid spacing based on projection.
  • nx -- The number of gridpoints in the X direction.
  • ny -- The number of gridpoints in the Y direction.

Example: PS 39.0 -97.0 2.3 2.3 25 17

An example of the header:

WXPGRID
WXP analysis for 15Z  6 AUG 98
2-Surface Temperature (F)
1 1 1 2 1 -9999 0 11:F
PS 43.00 -93.00 1.10 1.10 25 17
WXPGRID
24 hour Eta valid 12Z FRI  7 AUG 98
2-850 mb Temperature (C)
7 1 89 211 100 850 24 11:C
LC:90.00:-95.00:25.00:25.00:1.00 40.606583 -100.553223 0.812710 0.812710 93 65

Describing this example, the first three lines are self-explanatory. The grid description line contains the following information:

Grid source=7 -- National Meteorological Center (NMC)
Grid version=1 -- Version number 1.
Grid model=89 -- Eta model
Grid type=211 -- AWIPS grid 211
Level type=100 -- Pressure level
Vertical level=850 -- 850 mb
Forecast time=24 -- 24 hour forecast
Variable type=11:C -- Temperature in C

This is used by WXP to quickly determine grid type, variable and units.

The grid is a 93x65 Lambert conformal grid centered at 40.6 North and 100.55 West with a standard parallel of 25 North. The grid spacing is roughly 81 km.

Grid Data

Each successive line contains the gridded data in a real number format for the xx by yy grid. The data are placed in the file starting at the upper lefthand gridpoint, and the first xx pieces of data in the file contain the first row of data running from left west to east. Subsequent xx pieces of data are used for the next rows of the data file until yy rows are filled. If the output is ASCII, the output is using a generic format in scientific notation (%e).  If the output is binary (flag=3), the output is IEEE big endian floating point (4 byte).

EXAMPLES

WXPGRID
24 hour Eta valid 12Z FRI  7 AUG 98
2-850 mb Temperature (C)
7 1 89 211 100 850 24 11:C
LC:90.00:-95.00:25.00:25.00:1.00 40.606583 -100.553223 0.812710 0.812710 93 65
-1.39984131e-001
-1.39984131e-001
1.10015869e-001
3.60015869e-001
6.10015869e-001
3.60015869e-001
6.10015869e-001
1.11001587e+000
...

SEE ALSO


For further information about WXP, email technical-support@weather.unisys.com
Last updated by Dan Vietor on August 6, 1998