Garmin elevations in crisis.

[fossyant]

I appreciate for route planning, but this is looking at the device, and I don't pay too much attention as it's either for routing or just recording rides. When planning a ride, I will look at ascent if I don't know the area but that's with the mapping software.

 

[EckyH]

Atmospheric pressure derived is considered more accurate than GPS elevations. Only really a problem if you have a massive low or high pressure system moving rapidly across where you are.

My commute (roughly 25,5km one way) has 141 metres total ascent according to Openstreetmap.
The Garmin 840 I use to record those rides shows different values for nearly every commute.
Maximum were 218metres...

E.

 

[Ming the Merciless]

My commute (roughly 25,5km one way) has 141 metres total ascent according to Openstreetmap.
The Garmin 840 I use to record those rides shows different values for nearly every commute.
Maximum were 218metres...

E.

Right, and do all those routes take an elevation measurement at exactly the same locations every time? Trying to assess elevation gain is like fractals. A different number of trackpoints or measured at different locations and you will get different results regardless of gps or pressure derived.

 

[geocycle]

You need to get to know your route planner! I find Cycle.travel underestimates elevation compared to my wahoo by about 10-15%. It is worse in very undulating terrain and much closer in flatter or more consistent climbing. This is a classic interpolation issue and limited by the size of the servers doing the number crunching. It’s only a ‘problem’ in planning routes for the lunacy climbing challenge!

 

[EckyH]

Right, and do all those routes take an elevation measurement at exactly the same locations every time? Trying to assess elevation gain is like fractals. A different number of trackpoints or measured at different locations and you will get different results regardless of gps or pressure derived.

It's the same real route (not routing in the meaning of navigation via the Garmin device, so no predefined track points) every time. The only deviations are 2-3 metres beside the road to purchase some fruits or vegetables or to go brambling.
On the other hand I know that it isn't flat as flat can be and the biggest mountain here is the "dutch mountain". It's invisible for humans and has no descent, only an ascent as long as the whole distance. In both directions. Probably the bike computer data include that mountain...

E.

 

[Ming the Merciless]

It's the same real route (not routing in the meaning of navigation via the Garmin device, so no predefined track points) every time. The only deviations are 2-3 metres beside the road to purchase some fruits or vegetables or to go brambling.
On the other hand I know that it isn't flat as flat can be and the biggest mountain here is the "dutch mountain". It's invisible for humans and has no descent, only an ascent as long as the whole distance. In both directions. Probably the bike computer data include that mountain...

E.

The point is that it will vary every time and is to be expected. It is not measuring height at the same location each time. A metre here or there every few seconds soon adds up.

 

[Milzy]

Garmin 1040 and other Garmin devices guess the elevation by atmospheric pressure: barometric height "measurement".
Therefore I don't trust them not as high as I could throw them.

E.

Yep, I’m going back to wahoo, should have never left. Bolt 3 probably.

 

[Dogtrousers]

Garmin 1040 and other Garmin devices guess the elevation by atmospheric pressure: barometric height "measurement".
Therefore I don't trust them not as high as I could throw them.

E.

So what kind of altimeter would you trust? And what brand of device uses this splendid method?

Just curious,

 

[Milzy]

Could my device be going from sea level or is it just wrong adding more?

 

[HLaB]

On the club ride my Garmin 1040 which is fresh up dated showed more climbing than everyone.
What’s going on, my computer is the best one out of the group & they’re all saying mine is over reading?

You're a taller rider, bigger bike and it was an undulating ride so at every peak your computer was going that little higher. It all adds up 😉

 

[oldandslow]

There is an element of metaphysics in defining even what the right answer should be. If there's a small drop part way up the hill, do you count both part-hills or the total? How far apart to the two parts have to be before you do count them separately? To get silly, if a rough road bounces you up and down, do those ascents count? It's not obvious in all cases.

 

[Pblakeney]

There is an element of metaphysics in defining even what the right answer should be. If there's a small drop part way up the hill, do you count both part-hills or the total? How far apart to the two parts have to be before you do count them separately? To get silly, if a rough road bounces you up and down, do those ascents count? It's not obvious in all cases.

Simple. Accumulated from start to finish.
Chasing sections is a mugs game. (Too many cheats)

 

[Sea of vapours]

devices guess the elevation by atmospheric pressure: barometric height "measurement".
Therefore I don't trust them not as high as I could throw them.

Don't fly then! That would surely be very alarming, not trusting that the plane's altimeter is reading altitude quite accurately.

 

[EckyH]

So what kind of altimeter would you trust? And what brand of device uses this splendid method?

I'd trust an altimeter which uses GPS (or similar systems) to locate the position and calculates the altitude from the internal map. The location on my Garmin is fairly accurate. And no, I don't know which brand uses that method.
So I don't care much about the elevation accuracy of my bicycle computer and take it as guesstimations.

Don't fly then!

Good advise, thanks. Fortunately I don't fly anymore, but for other reasons.

E.

 

[Sea of vapours]

I'd trust an altimeter which uses GPS (or similar systems) to locate the position and calculates the altitude from the internal map.

That would be most unwise if it actually mattered (such as in a plane, which you're wisely avoiding for doubtless lots of good reasons). GPS altitude on its own is not especially accurate at a point in time (it is if a suitable sample set at a single point over time is used). GPS position horizontally is, as you say, very accurate, but the nature of the triangulation makes altitude rather less so and planes use barometric data (calibrated, frequently, etc.)