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Old 09-15-11, 06:21 AM   #1
donheff
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Garmin Edge 500 question

I recently picked up a Garmin Edge 500 and noted an anomaly that doesn't seem right to me. I'm hoping some of you tech oriented riders may be familiar with the device. On two rides from my house that I have recorded so far the elevation chart shows me starting out at zero height (OK so far) then accurately shows me going down a local hill, climbing other hills and whatever, then climbing as I return home but in both cases ends showing me about 100 feet higher than I started. It should be showing me back where I was when I began or am I missing something?
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Old 09-15-11, 06:57 AM   #2
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Mine will do this on occasion. Don't know for sure but it could calculate elevation based on barometric pressure so if the barometric pressure changes during your ride it would give you a different reading when you arrive home. But I don't know for sure.
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Old 09-15-11, 07:44 AM   #3
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Mine will do this on occasion. Don't know for sure but it could calculate elevation based on barometric pressure so if the barometric pressure changes during your ride it would give you a different reading when you arrive home. But I don't know for sure.

This.

Load your rides into Garmin Connect and it will 'fix' this based on the know surveys of the area - basically the maps know how tall a place is so it recalibrates your ride for you.
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Old 09-15-11, 08:17 AM   #4
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It'll never be perfect. Air pressure changes during a ride, and even the wind pressure on fast downhills can affect it's elevation calculations. I stopped for 20 minutes when a thunderstorm rolled through, and "gained" 200 feet as the pressure dropped. It's still close enough to give you a good idea of your ride elevations.

It's still more accurate than using GPS elevation calculations, since they need too many readings to be as accurate as air pressure. On my 705, I can do a "Save Location" and choose Average, wait about a minute while it calculates an accurate elevation via GPS, and save the location. Now if the location is within 100 feet (or 100 yards?) when I hit Start, it uses the accurate elevation, instead of the estimated elevation.

I never use the "fix" functions on the upload sites, since they really aren't any more accurate--they have to estimate the exact road elevations based on known elevation points near the road. And the "fix" tends to show more small bumps in the elevations, increasing the total elevation gain for the ride.

Last edited by rm -rf; 09-15-11 at 08:28 AM.
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Old 09-15-11, 09:06 AM   #5
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Thanks. I just assumed it was using GPS data. I entered my elevation for my home and will see if it makes a difference. It will be interesting to see how it deals with changing air pressure during an out and back ride with a set elevation for the start/finish.
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Old 09-15-11, 04:59 PM   #6
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Understand you are dealing with uncorrected air pressure and gps. You are not going to get something that is very accurate. I'd think that 100' is a very acceptable result.
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Old 09-15-11, 06:06 PM   #7
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Understand you are dealing with uncorrected air pressure and gps. You are not going to get something that is very accurate. I'd think that 100' is a very acceptable result.
+1 given where we were ten years ago, I'd say it is very acceptable for a cyclist.
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Old 09-15-11, 06:20 PM   #8
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It's still more accurate than using GPS elevation calculations, since they need too many readings to be as accurate as air pressure. On my 705, I can do a "Save Location" and choose Average, wait about a minute while it calculates an accurate elevation via GPS, and save the location. Now if the location is within 100 feet (or 100 yards?) when I hit Start, it uses the accurate elevation, instead of the estimated elevation.
The barometric readings are better at showing small differences in elevation, but due to changes in air pressure, are less accurate. The Garmin will correct the altitude calculated from air pressure in the course of a ride as it accumulates GPS readings. This can lead to altitude differences across the course of a ride.

I can't really figure out the elevation function. I set 3 elevation points in my very short driveway, and the elevation readings still are all over the place when I take off from there on a ride.
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Old 09-15-11, 06:40 PM   #9
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I bought one a week ago and have 4 rides where everyone my garage is either a few feet higher or several feet lower than when I left it.

Mine does the same thing.
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Old 09-15-11, 07:46 PM   #10
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The barometric readings are better at showing small differences in elevation, but due to changes in air pressure, are less accurate. The Garmin will correct the altitude calculated from air pressure in the course of a ride as it accumulates GPS readings. This can lead to altitude differences across the course of a ride.
I can't really figure out the elevation function. I set 3 elevation points in my very short driveway, and the elevation readings still are all over the place when I take off from there on a ride.
Yeah, small differences are accurate. I can see the elevation change as I walk up each step in my house. Anyway, local changes are more important for grade calculations. The whole ride can drift a few hundred feet over 30 or 50 miles, and it won't matter at all.


I would expect that Garmins would adjust their elevation at least when I was stopped for 30 seconds or more. But I don't see any pattern to it. Does it ever adjust the elevation using GPS during a ride? I don't know.

On the 705, the elevation needs to be nearby when I hit Start. It ignores stored elevations that I pass nearby after the route is started.
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Old 09-15-11, 09:36 PM   #11
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There is a forum on the Edge 500 at Garmen Connect that may have some discussion of this issue. Also, FYI:

http://www.dcrainmaker.com/2009/11/g...th-review.html
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Old 09-17-11, 01:17 PM   #12
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100 feet higher than you started? Then it's going to rain.

I think others have addressed your problem already, but the accuracy of your barometric altimeter will be better in stable weather and worse when there's a front moving through. As others have noted, if you want the elevation data from gps waypoints, you can toggle that option in Garmin Connect

Now, on to the question that you haven't asked. You will soon find that the Garmin Connect site basically sucks. The uploads take forever and the data manipulation is terrible. To get much more out of your gps data, export your ride as a tcx file and then upload it to RideWithGPS.com. Alternatively, you can now upload the data directly from your Garmin. Much more satisfying.
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Old 09-18-11, 06:51 AM   #13
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Now, on to the question that you haven't asked. You will soon find that the Garmin Connect site basically sucks. The uploads take forever and the data manipulation is terrible. To get much more out of your gps data, export your ride as a tcx file and then upload it to RideWithGPS.com. Alternatively, you can now upload the data directly from your Garmin. Much more satisfying.
Thanks MinnMan, I signed up. That is a great site.
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