canthidefromme

Sucks. Really, it sucks a lot. My "5000" ft of climbing is in reality 3200 ft of climbing when corrected by garminconnect.

Nbob

I may be wrong but you probably did do around 5000 ft. I think garminconnect may have an altitude smoothing feature in that it doesn't count any climb of less than x ft. Your GPS will count every small incline along the way but when you download it is smoothed to show only the hill like climbs ??

rallison

Which Garmin do you have?

umd

"correction" is not necessarily going to be better than the original data. If you have a unit with a barometric altimeter, you are generally better off leaving correction off. Which unit is it? Bow much elevation did it say on the unit before you downloaded it? Was the 5000 on GC without the correction, or in a different program like training center?

rallison

Very true. This is what I was getting at with my question. A GPS unit without a barometric altimeter will experience a significant amount of altitude float (just watch your elevation numbers as you climb...you will on occasion see your elevation go down up to 50 feet in one shot despite climbing for the entire duration). All this float leads to elevated elevation gain numbers. I've got a Forerunner 305 and have to deal with that. It gets annoying. On the other hand, online mapping elevation gain numbers also carry some error since the plotted roads do not always exactly track to the road itself. Usually, though, those numbers (basically the garmin corrected numbers) seem to be a little closer to reality than those from a non-barometric gps unit. And, of course, if you have an Edge with barometric altitude, that will probably be the most accurate.

byte_speed

A major source of error in elevation data is "jitter" in the data - small jumps up or down while the elevation is changing smoothly (or level). This could be from bumps in the road affecting the sensor or perhaps the pressure wave from a passing vehicle. If it wasn't for this "jitter", smoothing software wouldn't be needed. How the data is smoothed can makes big difference in the final numbers.

Also, the 305 ( and probably others) correct the barometric altitude using GPS, but it takes a while for the GPS to find the altitude. Garmin support told me this could take 20 minutes.

This can result in sizable jumps in elevation, I've seen 500 ft on occasion comparing the start and end elevations as I leave & return home. How the software handles these can lead to discrepancies.

logdrum

Doesn't a barometric altimeter fluctuate with temperature?

Beaker

As it's barometric, weather will affect it, my house often appears to change altitude after I've been out riding for a while. As to the OP I've come to the conclusion that there are no 100% accurate ways to track elevation, but I do tend to go with the BA reading from my 305 as it actually measures elevation differences. I believe that a lot of the data logging programs take your GPS coordinates and layer them over a topo map to then work out the elevation of your ride. If you've ever seen how your GPS path varies from roads on topo maps, it's hardly a surprise to see errors accumulate.

Brightwork

I almost always start and end at the same point. I've never had my feet of climbing match my feet of descent on my 705.

johnny99

Decent barometric altimeters have thermometers.

johnny99

I always turn my Garmin on 15 minutes or so before I start my ride to avoid this problem. I never have a 500 foot difference between begin and end altitudes. At most 100 feet, but that's maybe 1% of my total elevation gain, which is not significant.

Jitter is a much bigger problem with GPS altitude than with barometric. If I record a ride with both my Garmin (GPS + barometer) and my cell phone (GPS only), they will record almost identical distance, but the cell phone will show 50% to 100% more elevation gain. GPS cumulative elevation gain is pretty worthless.

RoboCheme

I start most of my rides from my home and I have my home's elevation entered into my Garmin. So basically it resets the elevation every time I hit the Start button. When I return, the elevation is never the same, but it's within + or - 20'. I correct the ascent reading from the Garmin and use that.

canthidefromme

I'm using my phone. Weirdest thing is, MyTracks (program on phone) says something different from Basecamp (which converts phone's gpx into one that garminconnect can read) says something different from Garminconnect (smoothed and unsmoothed) says something different from mapmyride.

I'm just gonna give up and say it was hard enough to warrant a compact.