Impossible speed and incorrect distance during snowboard activity

EgoIcti - attach the original .fit files in a reply to this post and I will remove the speed spikes for you.

cheers
Mike

Did you have 3D speed enabled?

I have disabled it on my watch in the skiing activity. It is a nice idea in theory, but it requires the vertical accuracy of the GPS to be much better than it actually is. Any noise in the altitude measurement will go directly into the speed calculation and cause too high speeds.

The error from not having 3D speed enabled is rather small. On a 25% grade (rather typical for a red slope in Europe), the theoretical error from not having 3D speed enabled is 6.25%. As you have already discovered, the error from having it enabled can be much, much higher.

EgoIcti - attach the original .fit files in a reply to this post and I will remove the speed spikes for you.

cheers
Mike

Thanks. You tool is useful. But activity synchronizing automatically after finish and I prefer to Garmin fix this bug.

Did you have 3D speed enabled?

I have disabled it on my watch in the skiing activity. It is a nice idea in theory, but it requires the vertical accuracy of the GPS to be much better than it actually is. Any noise in the altitude measurement will go directly into the speed calculation and cause too high speeds.

The error from not having 3D speed enabled is rather small. On a 25% grade (rather typical for a red slope in Europe), the theoretical error from not having 3D speed enabled is 6.25%. As you have already discovered, the error from having it enabled can be much, much higher.

Yes, 3D speed is enabled. I was thinks that this very important for mountain activities because high altitude changes. I like different slopes, and also black slopes with 70% grade.
But thanks for you advice. I will try disable 3D speed when skiing at small slope in my country. Nearby my home only 200m length slopes with very small altitude changes.

Garmin, I think this is not hard task to filter this GPS noise programmable. I seen many advertisements of Garmin watches in St. Anton in Austria. Customers will be upset with this bugs.

At 70% slope, the error without 3D speed is 18%. Still less than what you are experiencing with 3D speed on.

And to get the full 18% error, you have to move straight downhill, which I don't see many people doing on 70% slopes - they usually move a lot in zig-zag pattern so the effective slope of their track is reduced.

Not important, but at 25% slope I would say the error is more like 2.9%.

Not important, but at 25% slope I would say the error is more like 2.9%.

Actually, more like 3.0% (when defining slope as vertical distance divided by horisontal distance). But yes, my 6.25% was definitely wrong.