Garmins and Barometric Altimeters
feisty
Posts: 161
I have a Garmin 520 (which I think is superb) and I use a neoprene case
I did a ride this morning on a rare day off work without childcare responsibilities and the heavens opened. Unbelievable rain. When I got back and uploaded my ride to Strava it claimed that my elevation was higher at the end than the start. I used Strava's elevation correction so that's all fine but two questions:
1. Has anyone else had this and, if so, did the garmin work OK on the next (dry) ride?
2. Is there any way to turn off the barometric altimeter and just rely on strava elevation?
Thanks
I did a ride this morning on a rare day off work without childcare responsibilities and the heavens opened. Unbelievable rain. When I got back and uploaded my ride to Strava it claimed that my elevation was higher at the end than the start. I used Strava's elevation correction so that's all fine but two questions:
1. Has anyone else had this and, if so, did the garmin work OK on the next (dry) ride?
2. Is there any way to turn off the barometric altimeter and just rely on strava elevation?
Thanks
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I have a Garmin 520 (which I think is superb) and I use a neoprene case
I did a ride this morning on a rare day off work without childcare responsibilities and the heavens opened. Unbelievable rain. When I got back and uploaded my ride to Strava it claimed that my elevation was higher at the end than the start. I used Strava's elevation correction so that's all fine but two questions:
1. Has anyone else had this and, if so, did the garmin work OK on the next (dry) ride?
2. Is there any way to turn off the barometric altimeter and just rely on strava elevation?
Thanks
Happens often in really hefty rain.
Blow into the hole where the altimeter is - it will make your altitude go crazy temporarily, but will bring everything back under cotnrol.
When you upload dodgy data to Strava, you can press the elevation? bit and let Strava fix it. I did this for a ride on Saturday where the altimeter went crazy in the heavy rain. It did a good job of it.0 -
I have a Garmin 520 (which I think is superb) and I use a neoprene case
I did a ride this morning on a rare day off work without childcare responsibilities and the heavens opened. Unbelievable rain. When I got back and uploaded my ride to Strava it claimed that my elevation was higher at the end than the start. I used Strava's elevation correction so that's all fine but two questions:
1. Has anyone else had this and, if so, did the garmin work OK on the next (dry) ride?
2. Is there any way to turn off the barometric altimeter and just rely on strava elevation?
Thanks
Happens often in really hefty rain.
Blow into the hole where the altimeter is - it will make your altitude go crazy temporarily, but will bring everything back under cotnrol.
When you upload dodgy data to Strava, you can press the elevation? bit and let Strava fix it. I did this for a ride on Saturday where the altimeter went crazy in the heavy rain. It did a good job of it.
Yip spot on. Although it's not just the rain, as far as I'm aware it's the low pressure too - which obviously we're seeing a lot of at the moment. It'll sort itself out once (if) this bloody precipitation sods off soon. As marcusjb says - correct in Strava and you're good to go.0 -
I've have had this happen on longer rides where the weather's changed or when there is a front coming through.
I also find that it happens very often when descending in the rain, the hole will get blocked and it will record a flat elevation profile for the rest of the ride.
In any case Strava can fix it.0 -
thanks all0
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I use a 500 and came to the conclusion a long time ago that the altimeter was rubbish - indeed, when I got back from my ride earlier today, I uploaded to Garmin connect (I do not use Stava) and it told me that home was 37'ft ASL when I started out but -3ft when I got back. Like Strava, Garmin connect has the facility to correct elevation and I suspect they both use the same OS data, The 37ft is correct!Cannondale Synapse Carbon Ultegra
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Climbed 64ft on the turbo last weekend. Edge 510
There is an option on Strava to correct altitude. It does it automatically if you have an Edge that does not have a barometric sensor (my 200 didn't). I'm sure this same function can override the Edge's reading.0 -
What you have to remember is that the Garmin isn't measuring altitude directly - it's measuring air pressure, and then using that as a proxy for altitude. If, after a two hour ride, when you end up back where you started, an elevation difference simply means that the air pressure has changed. I've had a 40 mile ride be recorded as 2200ft of ascent and 2400ft of descent, and that was a ride that started and finished at home. My house doesn't have a really bad case of subsidence; it was just that the weather changed during the ride.
So, if the barometric proxy method is so inaccurate, why doesn't it use the GPS signal? Because that would be even worse!
GPS heights are based on an ellipsoid (a mathematical representation of the earth's shape), while USGS map elevations are based on a vertical datum tied to the geoid (or what is commonly called mean sea level). Basically, these are two different systems, although they have a relationship that has been modeled.
The main source of error has to do with the arrangement of the satellite configurations during fix determinations. The earth blocks out satellites needed to get a good quality vertical measurement. Once the vertical datum is taken into account, the accuracy permitted by geometry considerations remains less than that of horizontal positions. It is not uncommon for satellite heights to be off from map elevations by +/- 400 ft. Use these values with caution when navigating.
Taken from http://support.garmin.com/support/searchSupport/case.faces?caseId=%7B66f1b0a0-4cd6-11dc-4733-000000000000%7D0 -
As above, the altimeter tends to get ruined in wet weather, and you often see a continual rise or fall in elevation over the course of the ride as the air pressure changes. That can be fixed by saving 'elevation points' to your device- if you have a few dotted around your usual routes it will use the saved altitude at those points as calibration during the ride.
I only use the Strava elevation correction if the barometer data is completely haywire- Strava gets elevation info from Google, which in turn gets its altitude info from the American version of OS last I read. This is super accurate in the US, but everywhere else (including here) has a much higher error, which combined over a long ride can make the barometer the more accurate version.0 -
To be fair, I find Garmin to be pretty repeatable on my commutes though these are obviously pretty short rides. I have recently had a case of water in the tapping which screwed up the elevation on one of my F500 rides.
I used to hill walk with a Forerunner 305 (running wristwatch - no barometer) - it was very accurate at the peaks of Scottish hills where there was good visibility of the "horizon" and therefore better vertical resolution. I found most peaks were within a metre of the OS map which is good enough for me.
If you think the Garmin is a bit shaky, take a look at the Strava data from someone using an iPhone - it's hilarious - especially if you know the real elevation profile. The prime example was the Kessock Bridge - from sea level to around 40 metres - you can clearly see its profile on a Garmin but it's impossible on an iPhone. I suspect that's why some Strava segments are almost flat but are ranked as a Cat 4 climb.ROAD < Scott Foil HMX Di2, Volagi Liscio Di2, Jamis Renegade Elite Di2, Cube Reaction Race > ROUGH0 -
I suspect that's why some Strava segments are almost flat but are ranked as a Cat 4 climb.
I noticed one in Manchester city centre which was dead flat but Strava claimed it was a Cat 4 climb - there was some sort of discrepancy in the data so it had a vertical wall halfway along it.
Like this one https://www.strava.com/segments/1355031 - that's just not real0 -
I've have had this happen on longer rides where the weather's changed or when there is a front coming through.
Certainly on long days out with changeable weather things do go off.
Ideally, everyone should calibrate the altimeter when they leave the house (I do it manually, but I am interested in iron-clover's way of doing it).
Even then, if the weather is changeable, the elevation will become inaccurate.
However, if the weather is steady, I am always impressed with how accurate they are (helps when you are cycling somewhere with handy elevation markers on the top of each col!) and they're usually within a metre or two of the stated elevation (even when the elevation is expressed as accurately as this one in the Pyrenees!):
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As above, the altimeter tends to get ruined in wet weather, and you often see a continual rise or fall in elevation over the course of the ride as the air pressure changes. That can be fixed by saving 'elevation points' to your device- if you have a few dotted around your usual routes it will use the saved altitude at those points as calibration during the ride.
I never knew about this, a quick Google led me to this (in case it helps anyone):
https://support.garmin.com/support/searchSupport/case.faces?caseId=%7B6f9f9310-dbe8-11e1-dcef-000000000000%7D
So putting an elevation point at my house with the known elevation (that I already manually calibrate it to anyway (not every ride, not even every other ride!)) should do it all automagically.
Sounds brilliant!0 -
Climbed 64ft on the turbo last weekend. Edge 510
There is an option on Strava to correct altitude. It does it automatically if you have an Edge that does not have a barometric sensor (my 200 didn't). I'm sure this same function can override the Edge's reading.
Climbing on the turbo like that is quite common! Just need to select the workout option in Strava so it ignores it!0 -
Strava elevation correction can be hugely inaccurate. I've stated this before, but last year's Etape was c.4,500 m of climbing according to the Garmin (pretty accurate) and well over 7,000 m if elevation correction was used!
On Garmin Connect you can effectively toggle between elevation correction and original data.
On Strava, I think (but may be wrong) that once elevation 'correction' is used, you can't go back to the original data.
Wet weather does play havoc with the Garmin though - odd when you're climbing and it says you're descending!0 -
Strava elevation correction can be hugely inaccurate. I've stated this before, but last year's Etape was c.4,500 m of climbing according to the Garmin (pretty accurate) and well over 7,000 m if elevation correction was used!
This is because the corrected elevation will follow your exact GPS trace, so if your GPS trace wonders off a cliff face your elevation will show that (however briefly). This happens quite a lot in mountainous areas. When i was in Majorca last year all the people using GPS elevation were posting about 15,000ft elevation per ride. I had about 7,000ft from my 810. If you looked at their data you could see lots of spikes in elevation which accounts for the massive error.
So stravas elevation correction is a bit misleading as it can make it worse, so not corrected :roll: .0
