Question about wind speed data

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BillOsler
Posts: 116
Joined: Mon Apr 04, 2016 10:10 am

Question about wind speed data

Post by BillOsler »

Apologies if this has been asked before but I haven't found anything via search.
I have been trying to make sense of the wind speed data I see in my ride files. My impression is that the CSV files exported by Isaac report wind speeds that are different from the wind speeds recorded in FIT files by the ConnectIQ app.
My best guess at this point is that the CSV files exported from Isaac have a wind speed that is the estimated relative wind speed, meaning that the absolute wind speed would be equal to wind speed - bike speed.
My best guess is that the @wind data reported by the Connect IQ app and recorded in the FIT file is estimated absolute wind speed and that the wind perceived by the rider in motion would be the sum of bike speed and the @wind speed.
(obviously either way I am referring to the portion of the wind speed that is collinear with the direction of bike travel rather than the actual full vector representation)
Are those impressions correct?
Velocomp
Velocomp CEO
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Joined: Fri Jan 11, 2008 8:43 am

Re: Question about wind speed data

Post by Velocomp »

Sorry, I just stumbled across your post. My apologies for not responding until now.

The wind speed recorded in the CSV file is the total opposing wind speed caused by bike motion and ground wind.

Wind speed reported in ConnectIQ app is the ground wind speed (caused by nature and by drafting).

Wind speed is in the direction of motion. It is not the vector wind speed.
John Hamann
BillOsler
Posts: 116
Joined: Mon Apr 04, 2016 10:10 am

Re: Question about wind speed data

Post by BillOsler »

Thank you for the information. I was attempting to estimate the vector windspeed by combining direction-of-travel data from the GPS with headwind data from the Aeropod and using those pairs to find the direction with maximum headwind but as best I can tell there is enough data smoothing in the windspeed data that the type of estimates I was attempting don't work well.
Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: Question about wind speed data

Post by Velocomp »

Hmm...csv wind speed data is averaged over 1 second or 5 seconds (I don't remember which); either would seem to be very minimal averaging for what you are trying to accomplish.
John Hamann
BillOsler
Posts: 116
Joined: Mon Apr 04, 2016 10:10 am

Re: Question about wind speed data

Post by BillOsler »

I tried it with both the FIT file windspeed and the CSV file windspeed and never got results that made sense. During the process I did start to wonder whether a pitot tube at the front/center of the bike can measure accurate tail wind speed if the wind speed is greater than the bike speed. I don't think that's a frequent situation but could crop up from time to time
Velocomp
Velocomp CEO
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Joined: Fri Jan 11, 2008 8:43 am

Re: Question about wind speed data

Post by Velocomp »

BillOsler wrote: Tue Nov 17, 2020 3:00 pm I tried it with both the FIT file windspeed and the CSV file windspeed and never got results that made sense. During the process I did start to wonder whether a pitot tube at the front/center of the bike can measure accurate tail wind speed if the wind speed is greater than the bike speed. I don't think that's a frequent situation but could crop up from time to time
If tailwind speed is greater than bike speed the wind port won't provide accurate wind speed data. Our experience is that this is not a common issue; when there is a tail wind, most cyclists pedal faster, until they have an apparent headwind.
John Hamann
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