What is displayed in the Wind Speed field of the exported CSV files?

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

What is displayed in the Wind Speed field of the exported CSV files?

Post by BillOsler »

I've never been quite sure what exactly is displayed in the Wind Speed field of the CSVs that Isaac exports.
It appears that Golden Cheetah can access the Wind Speed data ... but whether it can use it in a meaningful way is unclear.
When Isaac exports the Wind Speed is it the measurement from the Pitot Tube or is it the estimated speed of the wind with respect to the ground?
Or, put another way, if there is no wind and I'm riding 20 mph will Isaac report a Wind Speed of 20 mph? Or zero?
I haven't found a good day to test this myself. It seems the wind is always blowing but I don't have a way to measure the ground speed of the wind.
Velocomp
Velocomp CEO
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Joined: Fri Jan 11, 2008 8:43 am

Re: What is displayed in the Wind Speed field of the exported CSV files?

Post by Velocomp »

It is the absolute wind speed.

So, if you're riding at 20 mph and there is no ground wind, the csv file will show a wind speed of 20 mph.
John Hamann
ted.kelly
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Joined: Fri Apr 19, 2019 12:40 pm

Re: What is displayed in the Wind Speed field of the exported CSV files?

Post by ted.kelly »

In sailing (where wind is very important) the accepted and long standing terminology is:
"apparent wind" is what an observer on a moving platform experiences.
"true wind" is what a stationary observer experiences (i.e. wind with respect to the ground)
So "apparent wind" is equal to "true wind" plus platform speed (well really vector subtraction i believe).
In the Issac software display options one can select "relative to the bike", "relative to the ground", or hide for wind.
It sounds like you are calling wind "relative to the bike" (what sailors, and I think pilots, would call "apparent wind") "absolute wind".
I think that is very confusing. How is the wind relative to the bike more "absolute" than the wind relative to the ground? Sounds perfectly backwards to me (i.e. wouldn't the "absolute" wind be the "true" wind and not the "apparent" wind). It might be better to leave the word "absolute" out of the thing entirely.

On a related notion, have you given any thought to developing a future version of AeroPod that measures crosswind (3 or 5 hole pitot tube, or wind vane) so you can determine total apparent wind speed, apparent wind angle, true wind angle and true wind speed? If you also had a bike heading (magnetic or geographic) you could get a real true wind direction.
Velocomp
Velocomp CEO
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Joined: Fri Jan 11, 2008 8:43 am

Re: What is displayed in the Wind Speed field of the exported CSV files?

Post by Velocomp »

I'm not a sailor (obviously), and as a non-sailor, I find the terms "apparent wind" and "true wind" to be quite confusing, too... :D

Going forward we will use the Isaac software terms, which are very descriptive:

Isaac "wind speed relative to the bike" = total wind speed 'felt' by cyclist, while riding, in the direction of motion = wind speed recorded in csv file = "apparent wind"

Isaac "wind speed relative to the ground" = wind speed 'felt' by the cyclist, while standing still, in the direction of motion = "true wind"
John Hamann
ted.kelly
Posts: 27
Joined: Fri Apr 19, 2019 12:40 pm

Re: What is displayed in the Wind Speed field of the exported CSV files?

Post by ted.kelly »

Yep, one thing I've found during a career in engineering is that clear unambiguous terminology that rarely confuses can be surprisingly hard to come by. I agree that the terminology you use in the Issac software is very descriptive and clear, and I applaud your choice to stick with it.
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