Garmin 800-Use Elevation Correction on Garmin Connect?
The Garmin website states the 800 has a barometer for calculating elevation and the data is accurate. On the Gamin Connect website, there is a button to use for "elevation correction" for devices. I recently did a ride and the 800 indicated I climbed 7300 ft., but when I hit the "elevation correction" button on the GC website, it changed to 11,000 ft. It sounds like with the 800 that the original data is more accurate. Can anyone shed some light on this, because I couldn't believe the difference was so significant. Below is what is posted on the GC website.
What are Elevation Corrections?
Elevation Corrections cross reference the horizontal position (latitude/longitude) provided by the GPS with elevation data that has been acquired by professional surveys. When corrections to elevation data are made, each trackpoint of your activity now contains the elevation from the web service, not the elevation provided by your GPS device.
Garmin Connect selectively applies corrections to depict a more realistic representation of your elevation experience. Activities recorded from devices without a barometric altimeter are enabled with Elevation Corrections by default. Alternatively, activities recorded by devices with a barometric altimeter generally contain accurate elevation data and therefore Elevation Corrections are disabled by default. For those users who are familiar with the MotionBased Gravity service, this is the same service.
normally, you wouldn't need to because the barometric altimeter is more accurate than the 30m DEM data GC uses for its corrections. Those are primarily intended for folks whose GPS receivers don't have a barometric altimeter.
HOWEVER, there are some situations where you might want to use it even though you had a barometric altimeter. For example, if you stopped midride and changing air pressure screwed up the rest of the ride, or if a weather system moving in caused all the data to skew. this is especially noticeable if your start/end points are far off from each other.
If you haven't already done it, setting up the virtual elevation points with the edge series will further improve results, as the auto-calibrate-from-GPS takes longer than half of my rides and I find it to be of dubious accuracy.
At the risk of sounding like a Garmin fanboy: Compared to the 1-minute elevation calibration of old with the etrex, it's awesome to just "pop" to the correct elevation as soon as you press start. I set a point in the parking lot at work and one at the base of my driveway from CGS survey points I had lying around, and 99% of all my rides start from one of those locations.
Thanks for both of these posts as they are very helpful. I must say that I've been very happy with my 800. I am a little bummed about the Vector Delay and as a result I've got 2 SRMs 1 Quarq and a power tap on my bikes
An interesting and valid point. When talking about the specific example of the OP, though, it probably wouldn't help much. I doubt that any weather change would cause a variation that would be equivalent to more than 3700 feet of elevation change, which is what it would need to be for your suggestion to help more than it would hurt in this particular case.
Originally Posted by NateHawk
Any such weather-based skew I notice in elevation measurements are never more than 200 feet or so (even across many days). And I would find it safe to claim that any elevation correction coming from DEM data would introduce errors much bigger than the maximum of 200 feet or so of weather-based skew that it's supposed to correct. So, like you said yourself, that feature should really only be used by those whose GPS records no elevation data at all, if you ask me.
I do something that's essentially equivalent. I use a bike computer as well as a sports watch, both with barometric altimeters. I know the precise elevation of the entrance of my garage. I always reset these two to that elevation in that spot before leaving for a ride. (The bike computer has a feature that makes it easy to reset the elevation to a preset default, and I do it manually on the watch.) I then manually calibrate my GPS altimeter at the trailhead to what the bike computer and watch show there. I believe the value to be trustworthy, because the two devices always show a value within 10 feet of each other at to the trailhead.
Originally Posted by ghettocruiser
(My reason for using both a bike computer and watch with altimeters is unrelated to this technique. It's only incidental that it also enables this approach.)
FWIW, I have seen a 1000ft elevation change due to weather before. and with my elevation at around 300ft, even a smaller 200ft change makes a big difference.