I have collected some GPS data from running over and around a hill many, many times.
The hill itself is about 9-10 meters high compared to the ground around it, although when I collected data, my altitude spanned about 25 meters.
I would like to be able to smooth the points so that I can describe the surface of the hill (latitude, longitude, and elevation). It's a bit cluttered, but I think it helps outline the paths that were taken, as well (I started with east-west rows, then north-south rows, then an inward spiral, then narrow figure-8s).
At points that are close to each other geographically, I noticed that there was quite a bit of variation over time. I took a look at the elevation over time, and I noticed that there was a drift:
There were a few breaks in time where I exited the bounds, usually to grab water, but for the most part the data uses 1-second intervals between each pair of points.
If it helps visualize the combination of the two graphs above, this version of the first graph uses 5 different shapes/facets for different bins of time. Keep in mind that I am running over the same region the entire duration, so the range of my altitude should be consistent over time if there weren't any drift.