GDTHGT draws contours and wind barbs or arrows on a time section at a
	point within a grid.

INPUT PARAMETERS
 
    GPOINT    *Grid point
    GDATTIM   *Grid date/time
    GVCORD    *Grid vertical coordinate
    GFUNC     *Grid function
    GVECT     *Grid vector function
    GDFILE    *Grid file
    PTYPE     *Plot type/h:w ratio/margins
    YAXIS     *Ystrt/ystop/yinc/lbl;gln;tck
    BORDER    *Background color/dash/width
    LINE      *Line color/type/width/label
    CINT      *Contour interval/min/max
    WIND      *Wind symbol/siz/wdth/typ/hdsz
    TITLE     *Title color/line/title
    CLEAR     *Clear screen flag
    SCALE     *Scaling factor
    PANEL     *Panel location/color/dash/width
    DEVICE    *Graphics device
    TEXT      *Text size/font/width/hw flag
 
 

PROGRAM DESCRIPTION
 
    GDTHGT is a user contributed program that draws a
    vertical time section at a location in a grid field.
    The location is specified by setting GPOINT.  Gridded
    data are interpolated to the time-section plane at regular
    intervals of time specified in GDATTIM.

    The grid vertical coordinate (GVCORD) may be PRES, THTA, or
    HGHT, depending on what is available in the grid file.
    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.

    Vector fields may be specified in GVECT and displayed as
    arrows or barbs.  The vector function CIRC cannot be
    computed for time sections.

    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.


EXAMPLES
 
    1.  Plot temperature in Celsius on a log-P chart on a
        time section from f00 to f24 at BWI.  Plot the contours
        in color number 2, using thick, solid lines.  Plot wind
        barbs for the forecast wind.  Plot the chart to 50
        millibars using the default labels.  Accept default
        values for the other parameters.

        GPOINT   =  bwi
        GDATTIM  =  all
        GVCORD   =  pres
        GFUNC    =  temp
        GVECT    =  wnd
        WIND     =  bm1
        GDFILE   =  gemdata:hrcbob.grd
        PTYPE    =  log
        YAXIS    =  /50
        CINT     =
        SCALE    =
        LINE     =  2/1/7
        BORDER   =
        TITLE    =
        CLEAR    =  yes
        DEVICE   =  xw
        TEXT     =
        PANEL    =


    2.  Now, using the same file, plot a log pressure time
        section of the vorticity advection, scaled by 10**9.
        Use a height-to-width plot ratio of 2.

        GFUNC   =  adv(avor(obs);obs)
        GVECT   =
        PTYPE   =  log/2
        SCALE   =  9
        WIND    =  am1


ERROR MESSAGES
 
    [GDTHGT  -1]   Fatal error initializing TAE.
    [GDTHGT  -2]   Fatal error reading TAE parameters.
    [GDTHGT  -3]   Fatal error initializing GEMPLT.
    [GDTHGT  -4]    Invalid vertical coordinate.
    [GDTHGT  -7]    Invalid axis type.
    [GDTHGT  -8]    Invalid vertical coordinate type.
    [GDTHGT -20]    Input for YAXIS is invalid.