 # Wind direction in UDP messages

For the Tempest hub’s ‘obs_st’ messages, is the wind direction parameter just a moment in time reading, similar to the ‘rapid_wind’ messages, or is it some kind of average of the direction over the reporting interval?

Thanks!

Everything in an observation (not an event) is an average over that observation’s time period, as far as I’m aware.

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From what David has indicated, the device takes a wind reading every three seconds and records it. The one minute reading is the calculated average of the 20 readings.

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So I averaged the direction degree values from the rapid_wind readings over the 1 minute interval and they aren’t matching up to the direction degree value in the obs_st readings… I was just doing a simple average though so I am not sure if that works on degrees… I did notice that the degrees in the last rapid_wind reading before a obs_st reading seem to be very close or often match, so it seems to me that its not an average, just the most recently measured direction reading…

Unfortunately a simple average does not work. You have to do a vector average. To illustrate, if the wind is blowing with a direction of 350 degrees for 3 seconds, and then it blows with a direction of 10 degrees for 3 seconds, we can instinctively see that the average direction is exactly 0 degrees. However, a simple arithmetic mean (350+10)/2 will give 180 degrees. This is not correct.

Similarly, the arithmetic mean of 0 and 360 degrees is also 180 degrees, despite the fact that 0 and 360 degrees are the same direction.

You can read more here and see the equation required to calculate the mean of circular quantities: https://en.wikipedia.org/wiki/Mean_of_circular_quantities

sure - but to answer the original question, it is an average value as calculated and reported by WF. Whether it’s a simple average or a weighted one doesn’t matter re: the original question in this thread - it’s an average value, not an instantaneous value.

Yes, I completely agree. I was just responding to this:

explaining why a simple average of the rapid_wind messages won’t match the 1 minute obs. The mis-match doesn’t mean that WF are taking an instantaneous value.