Garmin 705 climbing data

[Henry]

Apologies if this be covered elsewhere already.

On my Garmin 705 I've recently noticed inaccuracies on the climbing data. On short flat local commutes, I'm getting too many metres of ascent to be realistic. On a longer (well 30km) ride yesterday I got definately not enough climbing.

I upload my rides to Strava and sometimes Garmin Connect website, that's where my figures come from.

I always let the Garmin detect the satellites fully before commencing ride.

I read somewhere else about setting the height of your house above sea level in the Garmin unit, and this keeping things accurate? If so, how do you do that please?

Any other tips to get it reading altitude more correctly?

[Greenbank]

Any other tips to get it reading altitude more correctly?

Squint and take it all with a pinch of salt.

GPSes don't do elevations very well, and these errors are compounded when attempting to work out ascent. It's especially bad for predominantly flat rides.

Here's an elevation plot from my Forerunner 405 whilst I was playing 5-a-side football:

http://www.greenbank.org/misc/elev_football.jpg

Garmin Training Centre gave me 163m of ascent!

My Edge 705 also gives me ~40m ascent on my commute, despite it being almost pan flat as it's next to the Thames the entire way. I only go over 2 bridges so I can only account for ~10m of ascent.

[frankly frankie]

Flat terrain is always going to make an oscillating elevation line look worse.  Its a bit like the current UK economy.

A firmware update may be in order.  Googling - from this page -

One of the potential ways to address this issue is within the 705 itself. The last 2 firmware upgrades have a feature whereby the 705 will set the altitude to a previously entered waypoint value if you press Start when you are within 100 feet or so of the waypoint. As such if you generally start your rides (or start driving to a ride) from (for instance) home, just enter your home and it's altitude as a waypoint.
I have about 6-7 of my common ride start points entered as waypoints with altitude info and my 705 does a very good job of adjusting it's starting altitude to the waypoint altitude when I start out on the ride.

Though I must say, as a user of a Garmin that has more explicit calibration options - that I would have to be pretty obsessive about calibration to do better than the unit's own self-calibration routines, which I imagine are similar to what the 705 does by default.

[caerau]

Note that on Garminconnect (and Strava I think) you can enable elevation correction which basically looks at your route and compares it to relief maps and corrects it accordingly.

[Feanor]

When I submitted a GPS tracklog to the AAA man for consideration, he reckoned the elevations were a bit low and the altitudes recorded in the tracklog were replaced with SRTM3 ones. These were obtained by NASA on space shuttle flights, and are publicly available. The tracklog was then re-assessed.

[Henry]

Squint and take it all with a pinch of salt.

Good call it's only numbers after all  Yes I also done what you suggested in Strava Caerau, "correcting", seems more accurate.

[caerau]

Well, you get a different number - whether it's more correct or not I wouldn't like to say 

(I would hope it is though)

[bryn]

I've previously posted here that the Etrex30 cumulative elevation climbed display is just plain wrong.

I can climb a 100m hill (i.e. bottom at 30m and top at 130m) and watch the gradually increasing elevation be correctly registered as I climb, but the cumulative elevation display at the top of the hill might be only 60m instead of 100m.  Garmin told me to do a factory  reset: it destroyed all my carefully crafted settings (thanks Francis!) but didn't fix the problem. 

This is the opposite of the problems in the previous posts, which could just be a result of summing of all the +/- 1m jitter data items.

I now use my wristwatch altimeter to do the end-of-the-day cumulative (bragging) reading; it's not so good for the small moment to moment variations, but pretty reliable on a macro scale.

--
Bryn

[Greenbank]

When I submitted a GPS tracklog to the AAA man for consideration, he reckoned the elevations were a bit low and the altitudes recorded in the tracklog were replaced with SRTM3 ones. These were obtained by NASA on space shuttle flights, and are publicly available. The tracklog was then re-assessed.

Fair enough, but remember that depending on the terrain (gorges, cliff roads, etc) the SRTM elevations can be quite fictional too; they're interpolated data after all.

[Ningishzidda]

For AAA, do a 'contour count'.

All the minor ups and downs hidden between contour lines on the OS Pathfinder are 'incidental' to the main event of those 10%, 15% and 20% hills, and can be ignored.

[JonBuoy]

Note that on Garminconnect (and Strava I think) you can enable elevation correction which basically looks at your route and compares it to relief maps and corrects it accordingly.

I did this on Strava on last Monday's 705 ride log and it reduced the climb from 6001' to 3840' 

That'll teach me !

My 705 also drifts as mentioned here.