GDCROSS displays a vertical cross section of scalar and/or vector
        grids.


INPUT PARAMETERS
 
    CXSTNS    *Cross-section station line
    GDATTIM   *Grid date/time
    GVCORD    *Grid vertical coordinate
    GFUNC     *Grid function
    GVECT     *Grid vector function
    GDFILE    *Grid file
    WIND      *Wind symbol/siz/wdth/typ/hdsz
    PTYPE     *Plot type/h:w ratio/margins
    YAXIS     *Ystrt/ystop/yinc/lbl;gln;tck
    CINT      *Contour interval/min/max
    SCALE     *Scaling factor
    LINE      *Line color/type/width/label
    BORDER    *Background color/dash/width
    TITLE     *Title color/line/title
    CLEAR     *Clear screen flag
    DEVICE    *Graphics device
    TEXT      *Text size/font/width/hw flag
    PANEL     *Panel location/color/dash/width
    CONTUR    *Contour attributes
    FINT      *Fill interval/min/max
    FLINE     *Fill colors
    CTYPE     *Contour type:  C/F
 
 
PROGRAM DESCRIPTION
 
    GDCROSS draws a vertical cross section between two points
    in a grid field.  The cross-section path is a line segment
    on the grid projection plane joining the two points.  Gridded
    data are interpolated to the cross-section plane at intervals
    corresponding to approximately one grid increment.

    CXSTNS specifies the beginning and ending points of the cross
    section.  Each point may be entered as a latitude and longitude
    separated by a semicolon, as station identifiers or numbers or
    as x and y grid coordinates separated by a semicolon and
    preceded by @.  The two points are separated by >.

    The vertical coordinate, set in GVCORD, can be PRES, THTA, or
    HGHT.  The data must be stored in that vertical coordinate in
    the grid file.  No automatic vertical interpolation is included.
    The vertical axis scaling, set in PTYPE, can be LIN, LOG, KAP
    or STUVE.  STUVE and KAP are the same; SKEWT may not be entered.
    The plot aspect ratio and margins may also be entered in PTYPE.

    Both scalar and vector fields can be displayed in the
    cross-section plane.  Contour lines are drawn through the scalar
    field.  Vector fields may be depicted using arrows or barbs.

    If M is entered in WIND, winds will be displayed in meters
    per second unless the KNOTV operator has been specified in
    GVECT, in which case the winds will be displayed in knots.
    IF K is entered in WIND, the wind is displayed in knots.

    The line contours and filled contours are specified as in GDCNTR.

    Circulations can be displayed in the cross-section plane by
    specifying GFUNC = CIRC ( V, W ), where V is a vector field
    and W is the scalar vertical motion in the GVCORD coordinate.
    The horizontal component of the circulation is the tangential
    component of V.  The vertical component is W scaled up to
    account for the exaggerated aspect ratio of the display
    relative to that of the real atmosphere.  For the CIRC
    operator,  W is assumed to be pressure velocity in mb/s
    for PRES and THTA coordinates and cm/s for the HGHT coordinate.
    If the vertical component does not require scaling, the
    circulation can be specified explicitly in the form
    GVECT = VECR ( TANG ( V ), W )/VERT, where VERT is a flag
    indicating that the vector components should not be rotated to
    be north-relative.


EXAMPLES
 
    1.  Plot temperature in Celsius on a log-P chart along the
        cross section from BWI to LAX.  Plot the contours in
        color number 2, using thick, solid lines.  Plot wind
        barbs for the wind.  Plot the chart to 50 millibars using
        the default labels.  Accept default values for the other
        parameters.

        CXSTNS   =  bwi>lax
        GDATTIM  =  last
        GVCORD   =  pres
        GFUNC    =  tmpc
        GVECT    =  wnd
        WIND     =  bm1
        GDFILE   =  ngm.grd
        PTYPE    =  log
        YAXIS    =  /50
        CINT     =
        SCALE    =
        LINE     =  2/1/7
        BORDER   =
        TITLE    =
        CLEAR    =  yes
        DEVICE   =  ps
        TEXT     =
        PANEL    =
        CTYPE    =  l


    2.  Now, using the same file, plot a log pressure cross
        section of the vorticity advection, scaled by 10**9.
        Also, plot the ageostrophic circulation using arrows.
        Use a cross-section line from grid point (1,1) to grid
        point (10,20).  Use a height-to-width plot ratio of 2.

        CXSTNS  =  @1;1>@10;20
        GFUNC   =  adv ( avor ( wnd ); wnd )
        GVECT   =  circ ( age; omeg )
        PTYPE   =  log/2
        SCALE   =  9
        WIND    =  am1


ERROR MESSAGES
 
    [GDCROSS  +2]  Surface value of GVCORD is not available.
    [GDCROSS  +1]   WARNING.  There are no contour levels.
    [GDCROSS  -1]   Fatal error initializing TAE.
    [GDCROSS  -2]   Fatal error reading TAE parameters.
    [GDCROSS  -3]   Fatal error initializing GEMPLT.
    [GDCROSS  -4]   Input for CXSTNS is invalid.
    [GDCROSS  -5]   Input for GDATTIM is invalid.
    [GDCROSS  -6]   Input for GVCORD is invalid.
    [GDCROSS  -7]   Input for PTYPE is invalid.
    [GDCROSS  -8]   Graph coordinates are incorrectly defined.
    [GDCROSS  -9]   No points found for cross section.
    [GDCROSS -10]   LOG is not possible for this vertical coordinate.
    [GDCROSS -11]   Cross-section coordinates are invalid.
    [GDCROSS -12]   No levels--check input for GDATTIM and GVCORD.
    [GDCROSS -13]   @LEVEL in-line parameter is not allowed.
    [GDCROSS -14]   %VCORD in-line parameter is not allowed.
    [GDCROSS -18]   GVECT cannot be evaluated.
    [GDCROSS -19]   GFUNC cannot be evaluated.
    [GDCROSS -20]   Input for YAXIS is invalid.