Hi,
I'm using sports tracker on my bike, and I also have a cycling computer.
When I'm in the open, I can see the instantaneous speed beeing rather consistent between both the phone and the computer, this is good news.
When I'm in the woods, the phone speed is going haywire. I can easily understand that the he foliage is coming in the way of GPS reception. My problem is that, after a 30km ride, the overall distance on the phone can be off by as much as 10% below if I have spend a bit of time on forest trails.
I'm guessing there are missing point due to foliage and that the software is not able to extrapolate the distance between the shadowed areas.
One more thing is altitude : the GPS is such that when there's not enough sats in sight, altitude accuracy is very bad (by exporting the sportstracker track as GPX, I can see errors of 50 to 100m in very shadowed areas or when cycling under a bridge). Here again, the software could be smart enough to extrapolate that it is rather unlikely that, in cycling or running mode for example, anybody would make a 100m jump in 5 seconds, therefore provide a calculated data when the measured data is too impossible