Start/End point of run is same, but elevation shows 25' difference there

I actually oversimplified a bit (please see below*), but the main point is that somehow the watch didn't identify that it was pretty much the same spot on the earth that the run started and ended, and assigned an elevation 25 feet higher at the start than the end.

Potential complication - I am using a Stryd foot pod. Could it be Stryd's error? How can I trouble shoot to tell?

*The finishing point was 100 feet short of the starting point on this route that had an identical first and last 1/4 mile. The difference in elevation between the starting point and 100 feet later on the run was 2 feet according to the watch, which seems reasonably accurate by the eyeball test.

0 gasteropod over 6 years ago

GPS was never designed to provide altitude and is notorious for doing a bad job of this. Therefore higher end watches use a barometric altimeter instead. The problem here is that it is hard for the watch to know if the altitude is changing or if the pressure is changing. Therefore, it is not uncommon to see a different start and end elevation even when they are the same spot. You could say that since it's the same spot, the watch could know it should be the same, but it would have no idea where the inaccuracy was introduced, so this is not done. Imagine a circular route up and down a mountain in changing weather. It would be pretty much impossible for a watch to know if the measured elevation is changing due to a real elevation change or a pressure change.

0 renton82 over 6 years ago

I don't know however why Garmin can't use continuous calibration using DEM data... It would be perfect!

0 NeilJonesOnline over 6 years ago

Is DEM data available at sufficient resolution though? In flat open country this wouldn't be an issue, but it you're fell running or traversing a steep ravine for example, a 30m resolution could provide totally meaningless results. Also, assuming the data would have to reside on the watch for realtime processing, how much storage space would be needed to store it at a suitable resolution?

And thinking about it, what happens when you run across a bridge crossing a steep gorge?

Genuine questions, I really don't know.

0 renton82 over 6 years ago

Is DEM data available at sufficient resolution though? In flat open country this wouldn't be an issue, but it you're fell running or traversing a steep ravine for example, a 30m resolution could provide totally meaningless results. Also, assuming the data would have to reside on the watch for realtime processing, how much storage space would be needed to store it at a suitable resolution?

And thinking about it, what happens when you run across a bridge crossing a steep gorge?

Genuine questions, I really don't know.

You are right, but if garmin let us to decide, we can activate it in certain environments...

0 Notne over 6 years ago

Thanks for the comments guys. So be it!