GDCNTR draws contour lines through a scalar grid.

INPUT PARAMETERS
 
    GDATTIM   *Grid date/time
    GLEVEL    *Grid level
    GVCORD    *Grid vertical coordinate
    GFUNC     *Grid function
    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    *Graphics device
    PROJ      *Map projection/angles/margins
    GAREA     *Graphics area
    CLEAR     *Clear screen flag
    PANEL     *Panel location/color/dash/width
    TEXT      *Text size/font/width/hw flag
    SCALE     *Scaling factor
    LATLON    *Line color/dash/width/label/inc
    HILO      *Color/sym/rng/rad/cnt/int?
    HLSYM     *HILO text size/font/width/hw flag
    CONTUR    *Contour attributes
    SKIP      *Skip factor
    FINT      *Fill interval/min/max
    FLINE     *Fill colors
    CTYPE     *Contour type:  C/F
 
 

PROGRAM DESCRIPTION
 
    GDCNTR draws contour lines through a scalar grid computed
    using the GEMPAK grid diagnostic functions.

    Contours may be displayed as lines or as a color fill.
    If CTYPE is L (or 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 either
    F/L or 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 type is set
    to a single number, n, then every nth value will be labelled.

    The attributes of the color fill are specified in FLINE.
    FINT specifies the interval or levels for the color fill.
    The first color specified in FLINE fills values less than the
    first level; while the last color fills values greater than
    the last level.  Hence, 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 variables CINT and FINT specify 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. If no contour interval is
    entered, a default value which will generate 5 to 10 contour
    lines will be selected. The scaling will be done before the
    contour interval is computed.

    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.

    The HILO and HLSYM parameters control marking and labeling the
    values of relative maxima and minima.

    A map, lat/lon grid, and title may also be included.


EXAMPLES
 
    1.  Draw contours every 4 degrees through the 850-mb
        temperature field for the 24-h forecast time.  Negative
        values will be dashed using line type 3; every other
        contour line will be labelled; all the contour lines will be
        drawn in color number 1. The display area will be a Mercator
        map centered on Colorado.  The contours are drawn on a clear
        screen with a dotted map, dotted lat/lon lines every 5 degrees
        and no title.


        GDATTIM  =  f24
        GLEVEL   =  850
        GVCORD   =  pres
        GFUNC    =  tmpc
        GDFILE   =  ngm.grd
        PROJ     =  mer
        GAREA    =  co
        LINE     =  1/-3/1/2
        CINT     =  4
        SCALE    =
        MAP      =  1/10
        LATLON   =  1/10/1/1/5;5
        TITLE    =  0
        DEVICE   =  xw
        PANEL    =  0
        CLEAR    =  yes
        TEXT     =
        CTYPE    =  l

    2.  Now overlay dewpoint lines on the above plot. The contour
        interval is set to 5.  The lines will be drawn dashed
        using color number 2, with labelling and line types
        as above.  Only parameters which must be changed from the
        above definitions are shown. The title "Temperature and
        Dewpoint" is added in color 1.

        GFUNC    =  dwpc
        LINE     =  2/-3/1/2
        CINT     =  5
        CLEAR    =  no
        MAP      =  0
        LATLON   =  0
        TITLE    =  1//Temperature and Dewpoint

    3.  Now clear the screen and draw a color fill of the divergence
        of the gridded wind, alternating between color 3 and 7.
        Scale the data by 10**5 and use a default contour interval.
        Draw contour lines in color 2 using heavy, solid lines,
        labelling every contour level.

        GFUNC    =  div (wnd)
        CLEAR    =  yes
        CINT     =
        SCALE    =  5
        LINE     =  2/1/7/1
        FINT     =
        FLINE    =  3;7
        MAP      =  1
        CTYPE    =  f/l

    4.  Clear the screen and draw contours of 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.

	GFUNC	 =  avor (wnd)
	CLEAR	 =  yes
	CINT	 =  2
	SCALE	 =  5
	LINE	 =  2/-3/2
	HILO	 =  2;6/X#;N#/;4-28/5//YES
	HLSYM	 =  1.5;1/3/1;2


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.