Hi guys,

Borrowed a SATMAP 10 unit over the weekend for this event http://www.justgiving.com/EFOD-Cardiff and just wondering where you find the total ascent figure… On the Trip Log page, there are three figures under the profile drawing: Max Ascent (in red), Min Ascent (in blue), and Ascent (in black).

Now I thought the Ascent figure in black was total ascent for the ride, but when I put the route into Mapmyride, it comes back with a much lower figure. For example, for Saturday’s leg, the ASC figure was 16568ft, yet in Mapmyride (http://www.mapmyride.com/route/gb/Holyhead%20to%20Devil%27s%20Bridge/138128497946576932) the ascent figure came back as 5509 ft, which is a large difference.

Which value is correct….

Cheers,

Alex

Which value is correct….

As a guess, the bottom one.

Geoff,

Looking at them, that’s what I would say, but then what does the figure on the SATMAP unit relate to? I’m thinking it may be a combined up and down figure……

Alex

The black one is total ascent.

Elevation figures on a GPS should be taken with a pinch of salt, elevation is harder to triangulate accurately than position. I usually find an error of around 20% for total elevation gain. 200% seems quite a lot though!

I suspect it is the ascent recorded by the unit. If you consider that there will be some error in the height recorded at every point, the errors can be compounded to give a total ascent much greater than the actual up and down. I would have expected an alogirthm to smooth the data out though.

Having checked the settings the Altitude Data Source is from Maps, not from GPS. It’s currently loaded with 1:50000 OS maps..

the Altitude Data Source is from Maps, not from GPS

Mine too. Still get around a 20% error when I load it back up to Tracklogs.