[wxqc] Text to Degrees

[Victor Engel]

I'm not sure what an average wind direction even means. There are
probably many approaches to averaging wind direction. One would be to
imagine a line being drawn from an origin. The line is drawn one unit
in the direction of the wind for each time interval. The first line is
drawn from the origin. The next is drawn from the endpoint of that
line, etc. The average direction is then the direction of the overall
line from the origin.

Of course, this is not well defined. Consider if the wind direction
changed one degree every minute for 6 hours, in the same direction
each time. What you'd end up with is a polygon with 360 sides ending
up at the origin. Since it's at the origin, there is no direction.

Another approach would be to think of the directions as baskets on
corners of a 16-pointed scale. Each time you measure wind in a certain
direction, add an item to that basket. The average would then be the
direction the scale pointed, which would be the direction of the
center of gravity of the baskets.

But I'm not so sure average direction is even meaningful, except on
the short term, where it's relatively consistent. Then you can use a
simple average. In this case, what I do is add 180 degrees mod 360 if
the number is close to 0 or 360, then subtract 180 degrees again mod
360 after performing the average.

On 4/8/07, Norm Shea <Norm.Shea at kiawah-owners.org> wrote:
>
>
> Is there an accepted protocol determining the predominant wind direction by
> averaging?   I've converted wind directions from text to degrees using the
> basic format
>
>
> N     0
>
> NNE   23
>
> NE    45
>
> ENE   68
>
> E     90
>
> ESE   113
>
> SE    135
>
> SSE   158
>
> S     180
>
> SSW   203
>
> SW    225
>
> WSW   248
>
> W     270
>
> WNW   293
>
> NW    315
>
> NNW   338
>
>
>
> but I'm thinking that averaging is going to weight things.
>
>
>
> Thanks,
>
> Norm
>
>
>
> Norm Shea
> Director, Lakes Management
> Kiawah Island Community Association Inc
> 20 Kestrel Court, Kiawah Island, SC 29455
> Phone 843-768-2315 x 255  Fax 843-768-0298  Mobile 843-708-3608
> Norm.Shea at kiawah-owners.org --- www.kiawah-owners.org
>
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