Logging Tour Vert Geek-ery Questions

Micah - that's a really good idea. I'll break open that gpx file later today and then post it up when I get a chance.

Jason - I hear you on the frequency and position vs. accuracy.  From what you are saying regarding snow heights, a modern gps with map installed is cross referencing it's position with the listed height of that position on a map?

On Baker tour yesterday, with  minimal up and down, my friend's phone GPS came in at ~6700 feet of gain when there was just no way that seemed possible. The Sunnto logged it at 6130' which seemed way more inline with TH and turnaround elevations (3100'to 9100' with a few short up and down's thrown in).

On a final note, when I worked as a land survey tech we would use GPS for recording physical location (like on a property boundary survey) but never used GPS for elevations (as in setting cut/fill depths for an excavation contractor). The tolerances for that kind of work were super tight - error allowances of 0.05' or five-hundreths of a foot so to speak - GPS was not that accurate in elevation. I never considered that relevant for this topic but maybe has more relevance than once thought.

Thanks for the input to all who replied

I have the same problem and I believe it will not be solved soon. I assume that my vertical data is off by 10% either way.

I am not familiar with the software you are using, I use Google Earth, but it is very likely the elevation data comes from the same source: Space Shuttle SRTM data, which offers 30m vertical accuracy at 90m horizontal grid spacing. Elevation data is quite expensive to collect and the SRTM data is the one that is most accessible so it is safe to assume most of the mapping apps and programs are using this (they sometimes mention this in the About section or in the user manual).

There are more precise elevation models, it is widely accepted the military has much better data for at substantial parts of the world (where the "bad" guys live). There are claims that Google Earth is using this in some parts of the world but I have not seen it.

Anyway the 30m over 90m accuracy is pretty good in flatlands but can and does produce substantial errors in the mountains, it will easily miss 600 ft up or down along a jagged ridges that abound around here.

For backcountry use I'd argue that in therms of vertical accuracy altimeter is still the best (especially the ones with recording interval of 1 m), followed by readings obtained form a GPS track in programs like Google Earth (i.e using the SRTM data), followed by smartphones using signal triangulation and GPS, followed by GPS/smartphones calculating the vertical from just the GPS signal.

Anyway if you want to go super geeky this is a good place to start:
eros.usgs.gov/elevation-products

Also this is what Garmin says about GPS vertical accuracy (applies to GPS chipsets in smartphones as well):
support.garmin.com/support/searchSupport...dc-4733-000000000000 }

Have fun!