GPS Altitude Issues

I was planning on writing a rant about GPS and altitude problems.  I still will, but it will be tempered, from the start, by some quick internet searching on how to fix the problem.

My issue is that when I wear my Garmin ForeRunner 405 running or biking on an "out and back," it will often show very different elevations on the route.  Super frustrating.  I understand some of the technical side of it.  You can read here if you are interest as to why GPS is more accurate on the lat/long than the elevation, but its not necessarily an easy discussion.  GPS is reasonably complicated mathematically, but the theory is straightforward.

It turns out that there are technical solutions to this very technical problem.  Sites like Strava, for instance, do this correction in the background unless you ask them not to.  There is a fantastic post in their help area describing in detail what they do.  If you don't use Strava, all is not lost.

There are programs out there (such as GPS Visualizer) that will use the 2D representation and then map it to the "DEM (digital elevation model) database" to get the third dimension (or really, the elevation is what we care about).  Unfortunately, as described in the Strava post, the best DEMs only have 10M accuracy (which seems mind-bogglingly bad to me).

While there are solutions, it still seems as if Strava and others are not taking advantage of all of the data that could be brought to bear on the problem of determining surface elevation and thus I still feel justified in complaining that Garmin doesn't correct altitude errors when I import my data.  It would seem to me that there are portions of the surface of this earth that are well travelled by GPS-wearing folks like myself, that we ought to have accurate enough readings (from thousands of receivers) to detect a repaving of a trail or road.  Think the Washington and Old Dominion trail in northern Virginia.

Less on the fitness side and more on the house side, I'd like a 3" accuracy model of my lot.  I think that would be fantastic for modeling drainage and hardscaping/landscaping projects in the future.  Perhaps that model doesn't need to integrate with the rest of the earth, it would be kinda cool if it did.