NCL Website header
NCL Home > Documentation > Functions > Graphics routines

wmdrft

Draws weather front lines on the given workstation.

Prototype

	procedure wmdrft (
		wks [1] : graphic,  
		y   [*] : float,    
		x   [*] : float     
	)

Arguments

wks

An NCL workstation identifier specifying where you want to draw your front lines. The wks identifier is one returned either from calling gsn_open_wks or calling create to create a Workstation object.

y

A one-dimensional array specifying Y-coordinate values of points along the front line. If the internal parameter EZF is set to a non-default value (i.e. this function is being used in conjunction with an NCL mapping function), then the Y-coordinate values are assumed to be longitudes expressed in degrees. Otherwise the Y-coordinates are assumed to be in NCL data units. The Y-coordinates appear in the argument list here before the X-coordinates to be compatible with the ordering of the latitudes before longitudes in the case EZF is non-default.

x

A one-dimensional array specifying X-coordinate values of points along the front line. If the internal parameter EZF is set to a non-default value (i.e. this function is being used in conjunction with an NCL mapping function), then the X-coordinate values are assumed to be latitudes expressed in degrees. Otherwise the X-coordinates are assumed to be in NCL data units.

Description

The procedure wmdrft uses the WMDRFT routine from the Wmap package to draw weather front lines.

The specified coordinate values are used as control points for a spline curve fit. The curve passes through the given coordinates. If the front has little curvature, then only a few points need to be specified to get a nice smooth curve.

For details on drawing weather fronts, see the section on drawing front lines in the wmap documentation for the lower level utilities.

Certain parameters may be set to control the appearance of the front lines. The procedure wmsetp is used to set parameter values, and the function wmgetp is used to retrieve parameter values. The parameters applicable to wmdrft are:

EZF - to flag that wmdrft is to be used in conjunction with an NCL mapping function
ARC - length of the front line (retrieval only)
ALO - surface front or aloft
BEG - space before first symbol on front line
END - space after last symbol on front line
BET - space between symbols on a front line
COL - global color index
CFC - color index for cold front symbols
CS1 - calculated slope at beginning of front line
CS2 - calculated slope at end of front line
DWD - line widths for certain fronts
FRO - type of front
LIN - line widths for the more common fronts
NBZ - number of points along a Bazier curve
NMS - number of symbols along a front line
REV - reverses direction of front symbols
SLF - flag for end slopes
SL1 - slope at beginning of front line
SL2 - slope at end of front line
STY - specify type of symbols along a front line
SWI - widths of symbols along a front line
T1C - colors for tropical fronts
T2C - colors for tropical fronts
WFC - color index for warm front symbols

The procedure wmdrft does not call frame.

See Also

wmbarb, wmbarbmap, wmgetp, wmlabs, wmsetp, wmstnm

Examples

Example 1

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"

;
;  Draw a weather front and a couple of "High" symbols
;  on a satellite view map projection.
;
begin

;
;  Create a color map and an X11 workstation.
;
  cmap = (/                      \
            (/ 1., 1., 1. /),    \  ; 0 - White background.
            (/ 0., 0., 0. /),    \  ; 1 - Black foreground.
            (/ 1., 0., 0. /),    \  ; 2 - Red.
            (/ 0., 0., 1. /),    \  ; 3 - Blue.
            (/ 0., 1., 1. /),    \  ; 4 - Cyan.
            (/ 1., 0., 1. /)     \  ; 5 - Magenta.
         /)
  wks = gsn_open_wks("x11","test_wmap")
  gsn_define_colormap(wks,cmap)

;
;  Create a satellite view projection.
;
  map_resources = True
  map_resources@gsnFrame = False
  map_resources@mpOutlineBoundarySets = "National"
  map_resources@mpNationalLineColor = 1
  map_resources@mpGridLineColor = 0
  map_resources@mpCenterLatF =   40.
  map_resources@mpCenterLonF = -105.
  map_resources@vpXF = 0.06
  map_resources@vpYF = 0.90
  map_resources@vpWidthF = 0.88
  map_resources@vpHeightF = 0.88
  map = gsn_map(wks,"Satellite",map_resources)

;
;  Draw a stationary front.
;
  wmsetp("ezf",1)           ; Tell wmap we are using an existing map projection.
  wmsetp("lin",1.0)         ; Line width of front curve.
  wmsetp("fro","stationary"); Specify stationary front.
  wmsetp("cfc",3)           ; Use blue for the triangles.
  wmsetp("wfc",2)           ; Use red for the bumps.
  wmsetp("swi",0.04)        ; Increase the size of the bumps and triangles.
  xlat = (/  20.,   30.,   35.,   40.,  45. , 50./)   ; Latitudes.
  xlon = (/-195., -125., -115., -105., -95., -85./)   ; Longitudes.
  wmdrft(wks, xlat, xlon)   ; Draw front.

;
;  Draw a couple of High symbols.
;
  wmsetp("hib",4)              ; Cyan for background.
  wmsetp("his",1)              ; Black for shadow.
  wmsetp("hic",5)              ; Magenta for bounding circle.
  wmsetp("sht",0.02)           ; Increase size.
  xl = (/  50.,  50./)         ; Latitudes.
  yl = (/-105.,-145./)         ; Longitudes.
  wmlabs(wks, xl, yl, "HI")    ; Draw symbols.
  frame(wks)

end