Gravity/Elevation/Altitude Correction

The barometer in the Edge305 is only accurate if the atmospheric pressure is constant. Since the weather is always changing the altitude measured at a fixed position will change and get lower when there is high pressure and higher when there is low pressure. This is how mountaineers can know that good or bad weather is moving in. This was supposed to be the beauty of GPS that it was not subject to the same errors as barometric pressure and changes in sea level for nautical navigation.

In practice, barometric altitude is more accurate than the currently-available GPS, at least for the typical user of Garmin fitness devices. The Edge 705 tries to fuse the baro and GPS altitudes, but that has also proven to be problematic.

If you want to know an exact altitude of a summit, valley, anything in between, there is a high chance your elevation readings may be off on the 705 depending on your level of patience.

If you want to know how many feet you gained climbing and descending all day, then there a high chance your total gain/loss will be accurate on a 705.

I care only about the latter.

The features I used most on the Motion Based site were the elevation and distance correction, neither of which are currently on the Garmin site. I saw a mention that elevation adjustment was a possible future addition, but have seen no mention of the distance adjustment.
As others have noted, there is an elevation discrepancy - I normally start and finish at the same place but there can be up to 100 feet difference in gain and loss. Motion Based corrected that so there was almost never a difference of more than a foot or two.

Third party software to fix poor elevation / altitude...

I also had this issue with my 305 - basically if I waited long enough at the start of a ride then eventually the elevation would get accurate from the GPS signal. However by this time all my mates would be 5 minutes up the road.

During your ride the elevation gets more accurate and by the end you'll find your house had moved up or down by 30 metres.
The problem is similar to that of barometric drift - where the air pressure changes which makes the altimeter think you've moved up or down in elevation when you haven't. They both have the same solution.

Anyway to cut a long story short, 3D Route Builder from www.hybridgeotools.com can fix this problem! Load in your tcx file and...

Before


After


You may need to read the instructions to do this (shock horror) here.

And if your data is still bad then you can ask 3D Route Builder to update the elevation from Google Earth (can often be way better than GPS only elevation data).

Gravity/Elevation/Altitude Correction

I have a Forerunner 305 and my main problem with the elevation calculation is that I could go out for a run, my 305 could say 10.00km but it was actually 10.5 becuase it hasn't taken into consideration the hills up and hills down. MB was good at adjusting for elevation and adding the extra meters but GC isn't.

I heard there were plans to have this fixed. I hope it's coming soon :)

BR
Steve

Wow - you must be running up some steep mountains!
For a 10km run to become 10.5km the gradient over the whole distance would have to be more than 30%!!

The steepest hills I have run are 10% and even if I spent the whole 10km running up and down that hill the difference this makes to the overall distance is negligible (about 50m).

Remember: a2=b2+c2

Altitude you say...?

I live on the water in Miami, which the last time I checked was considered pretty much sea level. It is interesting to see sometimes that in a 45 mile bike ride i have climbed 11,000 plus feet. With the exception of being in the open desert I can't think of a better place for clear signal then where I am...I am away from any tall buildings riding along next to the ocean...very strange...perhaps Contador could come and train here...?

Steve

Gravity/Elevation/Altitude Correction

I usually run quite a few hilly forest runs. In training centre it shows me 10.00km. When I load the activity to Garmin Connect I get 10.00km but when I could upload to Moton Based I got the result 10.58 km for the same activity!

See attached jpg's

Regards
Steve

The Motionbased feature I recall gives you an option of using the device reading, which on a barometric unit is almost aways most accurate or using a known elevation pattern which never seemed proper to me, this feature is a must here for sports concerning climbing totals, the current deployment is of no use