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From: luong@tonto.DEC (Van Luong Nguyen  UHO  DTN 264-6560)
Newsgroups: net.puzzle
Subject: wind direction measurement
Message-ID: <2596@decwrl.UUCP>
Date: Mon, 16-Jul-84 11:17:05 EDT
Article-I.D.: decwrl.2596
Posted: Mon Jul 16 11:17:05 1984
Date-Received: Tue, 17-Jul-84 06:30:15 EDT
Sender: daemon@decwrl.UUCP
Organization: DEC Engineering Network
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Each reading of wind direction should of course be represented by a vector.
The vector points in the direction the wind is blowing, and the length of the
vector can represent the wind velocity. If wind velocity is not measured, all
vectors will be given unit length.

Several readings are averaged by vector addition.

The easiest way to do vector arithmetic is to remember that a vector of angle
A and length L, is equivalent to a complex number in the form c = (a + bi),
where  i  is the imaginary unit number (i squared = -1), and:

	a = L * cos A
	b = L * sin A

If wind velocity is ignored, then L = 1, and  a = cos A , b = sin A .

If n measurements yield readings c1 = (a1 + b1i), c2, c3, ...,cn , then the
average value c is given by:

	c = (1/n) [ (a1+a2+...+an) + (b1+b2+...+bn)i ]

On the XY plane with center O, c is represented by vector OC, where the
coordinates of C are:  x = (a1+..+an)/n ,  and  y = (b1+...+bn)/n.


Van Luong Nguyen,
Digital Equipment Corporation.
Nashua, New Hampshire.