How does a cycling computer know the gradient?

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Deleted member 121159

Guest
I was just thinking, huh, how is my Wahoo recording the gradients of every single bit of road I go on? Does it somehow calculate it itself? or does it communicate with a satellite map where this information is stored? If latter, who went and measured the gradients of all roads?! I guess it can't be that, cos it shows the gradient when you go off road as well. But how does it generate that data??
 

T.M.H.N.E.T

Rainbows aren't just for world champions
Location
Northern Ireland
Barometric altimeter built in vs GPS data
 

ColinJ

Puzzle game procrastinator!
I think it is calculated based on the elevation changes and distance between points. That means that the displayed gradient figure always lags behind somewhat. It used to drive me mad to be told that I was going down a 20% descent when I had actually done that 10 seconds ago to cross a bridge and was now climbing at 20% on the other side! I turned the gradient display off.
 
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Deleted member 121159

Guest
Ah of course, it's got a barometer inside. It was kind of stupid of me not to realise that!
 

ColinJ

Puzzle game procrastinator!
Ah of course, it's got a barometer inside. It was kind of stupid of me not to realise that!
It is possible for GPS devices without barometers to calculate elevation but usually with a fairly wide range of error.

Having said that, my old barometer-free Garmin Etrex typically got it within 20 metres or so, and my Edge 500 which does have a barometer is often out by more than that, despite me setting the elevation at home before setting off.
 

sleuthey

Legendary Member
It is possible for GPS devices without barometers to calculate elevation but usually with a fairly wide range of error.

Having said that, my old barometer-free Garmin Etrex typically got it within 20 metres or so, and my Edge 500 which does have a barometer is often out by more than that, despite me setting the elevation at home before setting off.

I have the cheapest smart phone you can buy in Argos. It runs Strava perfectly Inc elevation. The phone has a GPS but have always assumed the service pulls info from OS map data somehow to provide the elevation
 

ColinJ

Puzzle game procrastinator!
I have the cheapest smart phone you can buy in Argos. It runs Strava perfectly Inc elevation. The phone has a GPS but have always assumed the service pulls info from OS map data somehow to provide the elevation
I wouldn't try to rely on a phone signal in many of the more interesting cycling areas up here...!

O2 coverage map.png
 

sleuthey

Legendary Member
I wouldn't try to rely on a phone signal in many of the more interesting cycling areas up here...!

View attachment 670812

The old phone I use in the car for Android Auto has no SIM card, you can download the maps for some but not all aps.
 

freiston

Veteran
Location
Coventry
From what I understand, both barometric and GPS elevation calculation are problematic and not particularly accurate. Garmin Connect offers an elevation correction that uses survey data instead of device data. When applied, my total ascent/descent always goes down for a ride. My device is a Garmin Edge 530 and I understand that this uses barometric pressure.
I vaguely recall a thread on another forum where one of the members is a bit of an expert on digital mapping/navigation (he is behind a popular online cycle route planner website) and, as I recall it, he explained that online route planners also have discrepancies in ascent/descent stats due to algorithms used to deduce the route elevation from available (survey/map) data.
 

freiston

Veteran
Location
Coventry
It must be map data as well, since it will show you upcoming gradients as well as what you’ve ridden.

I wonder if and how they're "linked" - the upcoming gradient could be from map data but the "ridden" gradient might be from recorded GPS/barometer alone.
 
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Deleted member 121159

Guest
Also silly of me to forget that most online maps show elevation data, so grades should be able to be calculated from that too.

When I make a route on Komoot and ride it, the Wahoo always comes up with quite a bit higher total elevation - it'd go from say 2500ft to 3000ft. I always go by the higher number as that makes me feel better but now I'm not so sure if I should!
 
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