convert wind direction in true North to Math convention

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wave_buoys 2018-2-16

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回答： Mayra 2019-7-9

Hi all,

I am very confused about how to convert wind direction in true North to math convention (Trigonometric style). Could anyone offer some help?

Thanks

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Geoff Hayes 2018-2-16

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tanq - do you have any examples or can you provide some context? If the wind is coming from the north (0 degrees), is the "math convention" just

0 + 180 = 180 degrees

and then you convert that into radians? I'm assuming that the compass is like

              N
              ^
              |
         W < - - > E
              |
              S

And so a wind coming from the north has a direction towards the south i.e. 180 degrees along the y-axis. Likewise, a wind from the west is blowing to the east and so its direction would be

270 + 180 = 450 = 90 degrees

I suppose that given this angle you may want to determine the x- and y-components. Since the angle is relative to true north, then for wind coming from the north with speed ws

 theta = 180 (degrees)
 x = ws * sind(theta)
 y = ws * cosd(theta)

Or the above is wrong and isn't what you are looking for...

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Answer 1

Jim Riggs 2018-2-16

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编辑：Jim Riggs 2018-2-16

WindVector.JPG

Working with wind direction vectors can be confusing, because there are two different conventions which are both widely used.

Meteorologists tend to describe the wind direction as the direction "from" which the wind is coming. i.e. the direction you would be facing with the wind hitting you directly in the face.

But many engineers prefer to use a wind vector defined by the direction "toward" which the wind is going. This is the direction you would be facing with the wind hitting you in the back of your head.

As you can see, these two "directions" are opposite even though they are describing the same vector. So the first step is to determine whether you are using the "from" convention or the "toward" convention.

(If you have data from a meteorological source, the wind direction is probably "direction from") The rest is simple - just draw a picture of the problem.

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Image Analyst 2018-2-17

Or you could use mod() or rem(). Or use sind() and cosd() if you want to do operations on angles in degrees.

However I still don't know what, given an angle in degrees, "convert wind direction in true North to math convention" means. What is "math convention"??? You've got degrees, so what do you want? I still have no idea.

wave_buoys 2018-2-17

great thanks all for your contributions. I sorted out

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Answer 2

Mayra 2019-7-9

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I have been struggling with the same problem and I found an easy way to deal with this.

First you should convert your original data (direction with true north, i.e. clockwise and 0° at the top and wind intensity, I will call Direction and Wind) to cartesian coordinates.

[u,v] = pol2cart(deg2rad(Direction),Wind);

Then you convert it againd to polar coordinates but swaping u and v

[theta,rho]=cart2pol(v,u);

Now theta is the wind direction in polar coordinates, i.e. counterclockwise and 0° at right.