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WINDBARB

WINDBARB

Purpose

This is routine for drawing wind barbs on a map.

Author

FANNING SOFTWARE CONSULTING
David Fanning, Ph.D.
1645 Sheely Drive
Fort Collins, CO 80526 USA
Phone: 970-221-0438
E-mail: david@idlcoyote.com
Coyote's Guide to IDL Programming: http://www.idlcoyote.com

Graphics.

Calling Sequence

Windbarb, x, y, speed, direction

Required Inputs

x: The X location of the wind barb, expressed in data coordinates.
Positive X is pointing in EAST direction.
y: The Y location of the wind barb, expressed in data coordinates.
Positive Y is pointing in NORTH direction.
speed: The wind speed, expressed in knots.
direction: The wind direction in degrees clockwise from north. Winds from
the NE come at 45 degrees, and the wind "arrow" points in the
direction from which the window is blowing. (The wind arrow
points in the direction of the station circle, with the "barbs"
of the arrow at the end of the arrow from which the wind is coming.)

Keywords

ASPECT: The aspect ratio of the map or plot in the display window.
CLIP: A four-element array in normalized coordinates [x0,y0,x1,y1] giving
the lower-left and upper-right corner of a cliping rectangle. This
is normally the extent of your plot. See the example below.
COLOR: The name of the color to draw the wind barbs in. May be a vector
the same length as X.
LENGTH: The approximate length of the wind barb in normalized coordinates.
Will be set to 0.066 of the plot distance in the X direction by default.
MAP_ROTATION: The clockwise rotation in degrees of the map North from the
top of the plot. Will be set to 0.0 by default.
SOUTHERN_HEMISPHERE: Windbarb "feathers" are traditionally drawn in the clockwise
direction in the northern hemispere and countercolockwise in the
southern hemisphere. Default is "northern" type feathers. Set this
keyword to select "southern" type feathers.
STATION: Set this keyword if you want to draw the wind barbs with station symbols.
(Requires STATIONPLOT from the Coyote Library.)

Restrictions

Requires cgColor and STATIONPLOT from the Coyote Library:
http://www.idlcoyote.com/programs/cgColor.pro
http://www.idlcoyote.com/programs/stationplot.pro

Example

Window, Title='Wind Barbs', /Free
seed = -3L
lon = Randomu(seed, 9) * 360 - 180
lat = Randomu(seed, 9) * 180 - 90
speed = Randomu(seed, 9) * 100 + 5.0
direction = Indgen(9)*45
Erase, Color=cgColor('Ivory', !P.Background)
Polyfill,[0.1, 0.1, 0.9, 0.9, 0.1], [0.1, 0.9, 0.9, 0.1, 0.1], /Normal, Color=cgColor('light gray')
Map_Set, /Cylindrical, Position=[0.1, 0.1, 0.9, 0.9], Color=cgColor('Steel Blue'), /NoErase
Map_Grid, Color=cgColor('Charcoal', !D.Table_Size-2)
Map_Continents, Color=cgColor('Sea Green', !D.Table_Size-3)
Windbarb, lon, lat, speed, direction, /Station, Color='Indian Red', /Southern_Hemisphere
To clip the windbards that fall outside the plot, substitute these two lines
for the last line in the example above:
clip = [0.1, 0.1, 0.9, 0.9]
Windbarb, lon, lat, speed, direction, /Station, Color='Indian Red', Clip=clip

Modification History

Written by: David W. Fanning, 20 May 2003.
It has been called to my attention that the wind barbs are pointing
in *exactly* the wrong direction. Sigh... Rotated by 180 degrees. DWF. 8 June 2004.
Now someone complains that the *corrected* version is off by 180 degrees! Sheesh!
Clearly, I'm no meteorologist. Both lines of code are in the file. Please use the one
you like the best. :-) (Line 177-178) 20 July 2004. DWF.
Added a CLIP keyword so you can clip the output to the extend of your graphics plot. 12 Nov 2004. DWF.
Added THICK keyword 23 February 2005. DWF.
After further research, I've reverted to the direction specified originally.
And I have changed the "feathers" to point clockwise normally, and counterdlockwise
if the SOUTHERN_HEMISPHERE keyword is set. Here are my sources (21 July 2005. DWF):
http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/sfcobs/wnd.rxml
http://www.al.noaa.gov/WWWHD/pubdocs/windbarb.html
Fixed a small CLIP problem. 21 July 2005. DWF.

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