GPS and elevation (Read 441 times)

I just finished running a 4.5 mile loop that I run on a regular basis.  I was wearing my Garmin Forerunner 610 GPS watch. 

The Garmin Connect site tells me my total elevation gain is 463 feet (with their correction turned on) and 370 feet with their correction turned off. 

My running ahead upload tells me 1100 feet.

When I trace the route on the mapping tool on this site it tell me the gain is 830 feet.

When I trace the route on the USATF mapping tool it tells me 412 feet.

Any idea why these are all so wildly different?

I can't find the page with a good explanation at the moment, but here's a little bit. Somewhere on TopoFusions site, they give some more comparisons. A lot of the variation is a result of the way the device does it's thing, and each software package using its own algorithms. Distances vary also.

More importantly, I don't believe that the 610 has a built-in barometric altimeter. My experience with those types of gps units (FR305) is that the amount of elevation recorded on rolling terrain can vary widely, somewhat randomly (as tested on a flat abandoned railroad trail near me many times). The elevation profile shows non-existent hills. I've found it reasonably accurate on mountains.

At this point, I don't usually worry about it too much - other than being sure I'm using something with a barometric altimeter, preferably tied to a gps. (I've spent enough time trying to deal with it in the past) If I'm in the mountains (continuous climbs), I can usually find nearby contours on the map. If I'm on my rolling hills, I know about how much I'll get based on time and route - close enough for logging purposes.