GRBCALC

Sections

• NAME
• SYNOPSIS
• PARAMETERS
• DESCRIPTION
• EXAMPLES
• FILES
• SEE ALSO

NAME

grbcalc - GRIB model contouring program

SYNOPSIS

grbcalc [parameters...] filename

PARAMETERS

DESCRIPTION

This program contours model gridpoint data.  For the most part, this is data stored in GRIB format.  GRIB is a compressed binary format ideal for storing model data for operational visualization. This program is set up to adapt to many types of model and file formats.  The forecast time, level and variable parameters are set up to mimic GRIB parameters so that any model grid can be queried using grbcalc. In addition, there is a way of automatically piecing component grids together prior to display.  Then, based on a plot domain, forecast time, level and variable, a contour plot is generated. Overlay plots, contour plots and loops can also be generated if the appropriate options are set.

The program will display data from many model sources. The model type is specified using the model resource. The specified string is looked up in the model.lup file which cross-references the model value to a file naming convention. Also, if the model grids are divided up, this lookup file will detail how the grids are to be pieced together. In many cases, global models are split into 4 or even 8 subgrids. Contouring the entire global grid may not be necessary for small domains such as North America. As a result, specialized pieced grids can be developed such as avn_na which will direct grbcalc to search and piece together only those grids that affect North America. In other cases, a specific model grid file will contain grids for more than one grid domain. The lookup file can direct grbcalc to only use specific grids from a specific domain. This is the case with the ETA model which is broadcast in two grid types: 211 and 207 (for Alaska).

The programs starts off by prompting the user for input grid file name. The list of available grid files is based on the file name convention which is dependent on the model type and the file name tag associated with it. The tag can be specifically changed with the in_file resource. The user may specify the input file either via the command line of through the current resource.

Next, the program prompts the user for the forecast time. This is done through a forecast time menu which is specified in the grbcalc.tim file. Remember, each model type has a specific set of valid forecast times which is defined in the time file. Because of the breadth of models available, not all of the model types will be covered. Even though a menu does not list an appropriate time, it is still accessible be specifically stating the time on either the command line or at the menu prompt.

After the forecast time has been set, the vertical level is prompted for. A level menu is displayed which covers most of the usable levels. This can be tailored with the grbcalc.lev file. Again, each model has a set of valid levels and the menu may not give a proper list of levels.  If the level is unknown, a value of "miss" can be used and the program will search for the first grid that matches both forecast time and variable type.

The program will now prompt the user for the particular variable to contour. The program will show a menu of commonly used variables but many more are defined internally by the GRIB products and listed in the grbcalc.var file. The GRIB variables can be queried with the griblook program.

These parameters can be accessed by name if they have not been redefined in the grbcalc.var file. Otherwise, prepending a "+" to the variable name will guarantee these variables will appear.

There are several derived variables from this list which are defined in the grbcalc.var file. These include composite plots, overlay plots and computed grids.

The plot domain defaults to the domain of the grid unless changed through the plot_domain resource. The domain can be interactively changed using the mouse once the plot has been generated.

The program will now open the graphics window and start processing the data. The user will be prompted for the output device. Then the grid file is opened and data read in. The piecing of grids will be done at this time. Any additional computations are performed to produce a derived variable.. The background map will plot first unless the output is a color fill contour in which the map plots last. Then, the maximum and minimum of the grid are displayed for the user to pick an appropriate contour interval. Then, the contour or vector plot will display.

There are several plot types.  For contour plots, there is:

• ln - line contours
• dln - dashed line contours
• ndln - negative dashed line contours. All contours less than 0 are dashed. The breakoff can be reset with the con_base resource.
• cf - color fill contours.  These are contours where the areas between the contour lines are filled with a progressive color scheme. By default, this is a 15 color scale in which the colors wrap around if there are more than 15 color level.  The color scheme can be set by the color_fill resource.

For vectors:

• vect -- vectors/arrows
• strm -- streamlines
• barb -- wind barbs

When the plot is complete, output can be saved to a GIF image file, spooled to the printer or the plot can be zoomed.  When zooming the image, the plot will redraw to the new domain.  It will also add more stations to the plot depending on the size of the domain. When the user is finished with the plot, the enter key can be hit which closes the window and returns the user to the variable prompt.

Output Files

By default, this program does not produce output files.  If a raw or grid file output is desired, use the out_file resource to enable this.  By default, this will create a WXP ASCII raw or grid file depending on the plot type.  The out_file can be a filename, a file tag (lookup in file name convention file) or a name convention (with wildcards). The output can be GIF file by specifying gif as the file type. It may be desirable to turn plotting of when producing output files. To do this, specify none for the plot_type resource.

EXAMPLES

   grbcalc -mo=eta -cu=la -ft=h24 -le=500 -va=rvort -de=d -pl=cf -in=2

This contours the 500 mb relative vorticity from the ETA model's 24 hour forecast. The plot is color fill contours with an interval of 2.

   grbcalc -mo=ngm -cu=la -ft=h24 -le=850 -va=temp -of=wxp -pl=none

This will generate grid file based on the grd name convention.  A specific filename can be used instead of wxp.

FILES

• grbcalc.tim - the time menu
• grbcalc.lev - the level menu
• grbcalc.var - the variable menu and definitions

SEE ALSO

• griblook - the GRIB/grid query program
• contour - the grid contouring program
• vector - the grid vector plotting program