GECNTR draws filled step contour displays as well as lines.

INPUT PARAMETERS
 
    GDATTIM   *Grid date/time
    GLEVEL    *Grid level
    GVCORD    *Grid vertical coordinate
    GFUNC     *Scalar grid
    GDFILE    *Grid file
    CINT      *Contour interval/min/max
    LINE      *Line color/type/width/label
    MAP       *Map color/dash/width
    TITLE     *Title color/line/title
    DEVICE    *Device|name|x size;y size|color type
    SATFIL    *Satellite image filename(s)
    RADFIL    *Radar image filename(s)
    PROJ      *Map projection/angles/margins|drop flag
    GAREA     *Graphics area
    CLEAR     *Clear screen flag
    PANEL     *Panel loc/color/dash/width/regn
    TEXT      *Text size/font/width/hw flag
    SCALE     *Scalar scale / vector scale
    LATLON    *Line color/dash/width/label/inc
    HILO      *Color/symbol/rng/rad/cnt/intp
    HLSYM     *HILO txt size/posn/font/wdth/hw
    CLRBAR    *Color/ornt/anch/x;y/ln;wd/freq
    CONTUR    *Subbox/smooth
    SKIP      *Skip_cntr/skip_plt_x;skip_plt_y
    FINT      *Fill interval/min/max
    FLINE     *Fill colors
    CTYPE     *Contour type:  C/F, dot, eta, box
    LUTFIL    *Enhancement lookup table filename
    STNPLT    *Txc|mkc/mkt/mks/mkwd/hwfl|stnfil
 
 

PROGRAM DESCRIPTION
 
    GECNTR draws contour lines through a scalar grid computed
    using the GEMPAK grid diagnostic functions.  Contours may be
    drawn in any valid GEMPAK projection and may be overlaid on
    images.  GECNTR also draws diamond fills for eta terrain,
    ignoring fill points and will display dots at non-fill
    points for values greater than zero (used to display water
    or ice points) GECNTR also offers the choice of displaying 
    boxes instead of diamonds if that is preferred (with CTYPE=box).

    Set GFUNC = h or help and run the program for additional
    help information.

    When colors are generated automatically for the terrain
    display, a file called master.z2n is either read or created
    if it does not exist.  If it exists in the local directory,
    it is read.  This file contains a table allowing color
    numbers to be generated by interpolation given a set of
    terrain step heights.  If the file does not exist, the
    current step heights are used to generate the color number
    interpolation table.  When comparing models with different
    terrain steps, run this program on the model with the most
    steps first to generate the master.z2n file that will be
    used for generating the color numbers for the other models.
    This will assure that consistent colors will be assigned
    to comparable step elevations in all of the displays.  Make
    sure that no master.z2n file already exists when you begin.
    A message about reading or creating master.z2n is printed
    to indicate how the color numbers were generated.

    A list of times may be given in GDATTIM allowing animation
    of the contours.

    Contours may be plotted in different display windows by specifying
    a name for the XW driver in DEVICE.

    Contours may be displayed as lines or as a color fill.
    If CTYPE is C, contour lines are drawn using input from CINT
    and LINE.  If CTYPE is F, filled contours are drawn using
    specifications from FINT and FLINE. Both contour lines and
    filled contours are drawn if CTYPE is F/C.

    The attributes of the contour lines, including the color,
    line type, line width, and label frequency are specified
    in LINE.  The four attributes must be separated with slashes;
    semicolons separate the values for each attribute.  If the
    line type is set to a single negative number, negative
    contour values will have the absolute value of the line type
    and positive values will be solid.  If the label frequency
    is set to a single number, n, then every nth value will be
    labeled.

    CINT specifies the contour interval, minimum value, and maximum
    value separated with slashes.  A scaling factor may be entered
    in SCALE. The data in the grid file will be multiplied by
    10 ** SCALE before the contour levels are selected.  If no
    contour interval is entered, a default value which will generate
    5 to 10 contour levels will be selected.

    The contour fill intervals are specified in FINT; the attributes
    for the fill are specified in FLINE.  The first color specified
    in FLINE fills values less than the first level; while the
    last color fills values greater than the last level.  Therefore,
    n levels require n+1 colors.

    A range of colors may be specified in either FLINE or LINE by
    specifying starting, ending and increment values in that order
    separated by dashes.  If the increment is missing, a default
    of 1 is used.

    The HILO and HLSYM parameters control marking and labeling the
    values of relative maxima and minima.  CLRBAR allows a color bar
    to be added for color fill contours.

    The SKIP parameter specifies the number of grid points to skip
    in generating contours.  For example, if SKIP = 1, every other
    point is used to generate the contours.

 
EXAMPLES
 
    1.  Draw contours every 2 degrees through the 700 mb
        temperature field for all of the forecast times.  Negative
        values will be dashed using line type 3; every other
        contour line will be labeled; all the contour lines will be
        drawn in color number 3. The display area will be a enlarged
        Mercator map centered on New York.  The contours are drawn on
        a clear screen with a map in dash pattern 7, dotted lat/lon
        lines every 5 degrees and no title.

	GDATTIM	 =  all
	GLEVEL	 =  700
	GVCORD	 =  pres
	GFUNC	 =  tmpc
	GDFILE	 =  $GEMDATA/hrcbob.grd
	CINT	 =  2
	LINE	 =  3/-3/1/2
	MAP	 =  1/7
	TITLE	 =  0
	DEVICE	 =  xw
	SATFIL	 =
	RADFIL	 =
	PROJ	 =  mer
	GAREA	 =  ny-
	CLEAR	 =  yes
	PANEL	 =  0
	TEXT	 =  1
	SCALE	 =  999
	LATLON	 =  2/10/1/1/5;5
	HILO	 =
	HLSYM	 =
	CLRBAR	 =
	CONTUR	 =  3
	SKIP	 =  0
	FINT	 =  0
	FLINE	 =  10-20
	CTYPE	 =  C
	LUTFIL   =
	STNPLT   =

    2.  Now overlay dewpoint lines on the above plots. The contour
        interval is set to 5.  The lines will be drawn in color 17,
        with labeling and line types as above.  The map and lat/lon
        lines will not be drawn for the overlay.  The title, which
        includes the date, level and the string "TEMPERATURE AND
        DEWPOINT", is added in color 1.

	GDATTIM	 =  all
	GLEVEL	 =  700
	GVCORD	 =  pres
	GFUNC	 =  dwpc
	GDFILE	 =  $GEMDATA/hrcbob.grd
	CINT	 =  5
	LINE	 =  17/-3/1/2
	MAP	 =  0
	TITLE	 =  1//~  @  TEMPERATURE AND DEWPOINT
	DEVICE	 =  xw
	SATFIL	 =
	RADFIL	 =
	PROJ	 =  mer
	GAREA	 =  ny-
	CLEAR	 =  no
	PANEL	 =  0
	TEXT	 =  1
	SCALE	 =  999
	LATLON	 =  0
	HILO	 =
	HLSYM	 =
	CLRBAR	 =
	CONTUR	 =  3
	SKIP	 =  0
	FINT	 =  0
	FLINE	 =  10-20
	CTYPE	 =  C
	LUTFIL   =
	STNPLT   =

    3.  Now clear the screen and draw a color fill of the divergence
        of the gridded wind, alternating between color 23 and 19, for
        the 24 hour forecast time.  Scale the data by 10**5 and use a
        contour interval of 0.5.  Draw contour lines in color 2 using
        heavy, solid lines, labeling every contour level. Draw a
        color bar of the fill colors using the default conditions.
        The display area is changed to Missouri and the lat/lon lines
        are plotted at 5 degree intervals.

	GDATTIM	 =  f24
	GLEVEL	 =  700
	GVCORD	 =  pres
	GFUNC	 =  div(wnd)
	GDFILE	 =  $GEMDATA/hrcbob.grd
	CINT	 =  .5
	LINE	 =  2/1/7/1
	MAP	 =  1
	TITLE	 =  1
	DEVICE	 =  xw
	SATFIL	 =
	RADFIL	 =
	PROJ	 =  mer
	GAREA	 =  mo
	CLEAR	 =  yes
	PANEL	 =  0
	TEXT	 =  1
	SCALE	 =  5
	LATLON	 =  0
	HILO	 =
	HLSYM	 =
	CLRBAR	 =  1
	CONTUR	 =  3
	SKIP	 =  0
	FINT	 =  .5
	FLINE	 =  23;19
	CTYPE	 =  f/c
	LUTFIL   =
	STNPLT   =

    4.  Clear the screen and draw contours of absolute vorticity.
        Label vorticity maxima with a red X and minima with a cyan N.
        Plot the values of the extrema.  Exclude minima less than
        4 * 10 ** -5.  The search radius for finding extrema is
        5 grid points.  Interpolate the extrema to off-grid point
        locations.  Plot the values in font number 2 on the
        right beneath the marking symbol.  Plot the marking label
        in size 1.5, the values in size 1.

	GDATTIM	 =  f24
	GLEVEL	 =  700
	GVCORD	 =  pres
	GFUNC	 =  avor(wnd)
	GDFILE	 =  $GEMDATA/hrcbob.grd
	CINT	 =  2
	LINE	 =  2/1/2
	MAP	 =  1
	TITLE	 =  1
	DEVICE	 =  xw
	SATFIL	 =
	RADFIL	 =
	PROJ	 =  mer
	GAREA	 =  ri
	CLEAR	 =  yes
	PANEL	 =  0
	TEXT	 =  1
	SCALE	 =  5
	LATLON	 =  0
	HILO	 =  2;6/X#;N#/;4-28/5//yes
	HLSYM	 =  1.5;1/3/1;2
	CLRBAR	 =  1
	CONTUR	 =  3
	SKIP	 =  0
	FINT	 =  2
	FLINE	 =  23;19
	CTYPE	 =  f/c
	LUTFIL   =
	STNPLT   =

ERROR MESSAGES
 
    [GDCNTR  +1]    WARNING.  There are no contour levels.
    [GDCNTR  -1]    Fatal error initializing TAE.
    [GDCNTR  -2]    Fatal error reading TAE parameters.
    [GDCNTR  -3]    Fatal error initializing GEMPLT.
    [GDCNTR  -4]    Grid requested is not available.
    [GDCNTR  -5]    Error setting grid navigation for file ....
    [GDCNTR  -6]    There are no grids in grid file.
    [GDCNTR -13]    There are no times in the grid file
