Originally Posted by
chong67
I know you wrote this last year, but your comment on elevation error on GPS phone still hold true or not? I can see grade numbers and % elevation on uphill/downhill/flatland on my android app. I wonder if this info come from Google topology map?
Still true. The user's spatial relationship with the GPS satellites makes it less sensitive to elevation than lat/lon. Strava, for example, throws away your GPS elevation data and uses topo data instead (which is why if you climb a 100' bridge in Strava, it won't show up in your climbing stats).
That said, GPS can detect elevation ... there is just a lot of short-term error (noise) in the data. On a long continuous climb or descent, a good filter algorithm can smooth out that noise and give you a fair estimation of % grade. In the flats or short rolling hills, it will be far less accurate. [MENTION=101834]njkayaker[/MENTION] is right about pressure sensors. They're actually getting pretty common in flagship phones. They have their own problems when used as altitude sensors, but generally produce better elevation data than GPS.