Garmin 500 elevation

[philinmerthyr]

The elevation on my Garmin 500 was around 400ft out today. I live at 600 ft above sea level but today my ride started at 196 ft and I dropped to -400 ft as I rode down to Cardiff. This would mean Cardiff would be flooded.

It has always been right in the past. Has anyone else had this happen.

I think the ride elevation was right just the start point was wrong.



http://app.strava.com/activities/65334988

 

[Nigelnaturist]

The elevation on my Garmin 500 was around 400ft out today. I live at 600 ft above sea level but today my ride started at 196 ft and I dropped to -400 ft as I rode down to Cardiff. This would mean Cardiff would be flooded.

It has always been right in the past. Has anyone else had this happen.

I think the ride elevation was right just the start point was wrong.



http://app.strava.com/activities/65334988

You can set elevation points, for the most popular start places you ride from 10 I think, I have a few set. The thing is the barometer altimeter is effected by the temp as well, so it is an idea to place the unit on the bike some time before you set off, garmin connect can also correct this, though you will end up with a different elevation gain. Strava and RWGPS also have this feature, but they are all different and will all be different to the units raw data.
One other thing if you stop for any length of time, the elevation will more than likely be effected, usually losing elevation.
To set the elevation, you need to know the altitude of where you are and then set it, there is software to do this (sporttracks with a plugin), I haven't come across anything else yet, maybe someone will point me in the right direction.

 

[Enw.nigel]

The elevation on my Garmin 500 was around 400ft out today. I live at 600 ft above sea level but today my ride started at 196 ft and I dropped to -400 ft as I rode down to Cardiff. This would mean Cardiff would be flooded.

It has always been right in the past. Has anyone else had this happen.

I think the ride elevation was right just the start point was wrong.



http://app.strava.com/activities/65334988

I can tell you that Cardiff wasn't flooded this morning when I set out. However. my Garmin 705 showed - 350 ft when it should read +108 ft. So a similar error on mine. Back home, it now reads +108. I must work out to set the start elevation as Nigelnaturist has mentioned.

 

[Nigelnaturist]

I can tell you that Cardiff wasn't flooded this morning when I set out. However. my Garmin 705 showed - 350 ft when it should read +108 ft. So a similar error on mine. Back home, it now reads +108. I must work out to set the start elevation as Nigelnaturist has mentioned.

I sometime go deep sea cycling, even though the nearest coast is about 40 miles away and thats only an estuary, and that is having it auto detect the height at home, its not a perfect system, but then nothing is.

 

[Louch]

i check it at start, if it looks off i switch off and n which tends to correct it. you can also correct it when you upload to garmin site

 

[Ccchicane]

Looked up this exact problem on some garmin forums, was advised to switch on the unit for about 10 mins before setting off ( when pumping tyres, filling bottles etc) and the unit should auto correct, I've been doing this since and have had no more minus elevations! Hope this helps

 

[Nigelnaturist]

My abortive ride tonight, had me 390ft under the sea, I am at 172ft above, and thats with the unit being on the bike a while.

 

[MaxInc]

The reason for that is that barometric altimeters can only provide relative altitude and not absolute readings. They can tell you how much the elevation has changed but not what the current elevation is. They only measure differences in air pressure which then later compare to a reference that was preset during calibration. They should have a means of calibrating them, some of them do it automatically based on know altitudes for particular GPS coordinates, usually the home location, which they will use to correct the daily variations on air pressure caused by weather fluctuations.

In this case it is a matter of finding the correct calibration procedure for your device. It is however safe to assume that the amount of climb during the ride should be as accurate as the device can be during normal operation.

 

[Nigelnaturist]

The reason for that is that barometric altimeters can only provide relative altitude and not absolute readings. They can tell you how much the elevation has changed but not what the current elevation is. They only measure differences in air pressure which then later compare to a reference that was preset during calibration. They should have a means of calibrating them, some of them do it automatically based on know altitudes for particular GPS coordinates, usually the home location, which they will use to correct the daily variations on air pressure caused by weather fluctuations.

In this case it is a matter of finding the correct calibration procedure for your device. It is however safe to assume that the amount of climb during the ride should be as accurate as the device can be during normal operation.

Its still effected by air temp, or the temp flowing over it as you ride, very rarely do I get a gain/loss elevation that is within 10-20ft. Even if I leave it setup and calibrated for my home altitude, and as previously mentioned, if you stop, in my case at the photo group ect. this will effect the elevation, if you look at a graph based on time not distance you can see how it changes, on distance it will show as a step.

 

[MaxInc]

Its still effected by air temp, or the temp flowing over it as you ride, very rarely do I get a gain/loss elevation that is within 10-20ft. Even if I leave it setup and calibrated for my home altitude, and as previously mentioned, if you stop, in my case at the photo group ect. this will effect the elevation, if you look at a graph based on time not distance you can see how it changes, on distance it will show as a step.

Indeed, that's why the data is not that accurate. However the weather variations during a few hours bicycle ride are much smaller compared to variations that can occur from day to day or between several days. This is how you can get the sort of errors that OP was experiencing.

 

[Nigelnaturist]

I haven't really took much notice of the initial elevation as I have always had it set to auto detect, the longer I leave it before setting off the more accurate it seems to be. I have had tracks which even when correct on garmin connect, have shown to be minus elevation ( I recall at least one). They shouldn't change over the space of 10-15 mins if you stop for example at a cake stop, but they do.
It's a bit pointless using these units for anything other than a guide for the elevation.

 

[HLaB]

With my old 305, I would cycle to the meet point 10 mins away and start the clock, aswell as allowing time for the gps to calibrate, it also meant that a track posted on Garmin Connect didn't lead to my front door

Edit I find the newer 800 to be more accurate/ calibrate faster and Strava sorts out the privacy issue.

 

[Nigelnaturist]

With my old 305, I would cycle to the meet point 10 mins away and start the clock, aswell as allowing time for the gps to calibrate, it also meant that a track posted on Garmin Connect didn't lead to my front door

Edit I find the newer 800 to be more accurate/ calibrate faster and Strava sorts out the privacy issue.

I start it at the end of the lane, I generally only ride from there to there, but as I said before if I am at a group, the difference in temp causes fluctuations, though I have both groups I go to set as elevation points, and I usually wait 5-10 mins before setting off (usually a cig).