Garmin 500 elevation issues

le_boss

Just wondering if anyone has noticed any elevation anomalies on the garmin edge 500 recently??

over the last month or so mine seems to record much lower elevation figures than i would expect.
easy enough to sort once uploaded to garmin connect (through the elevations correction option) but still annoying.

its also worth noting that my start point is recorded as being at 400ft on the garmin, but where i live is actually 600ft.
prior to the past month this was always accurate, just isnt at the moment.

anyone else noticed this?

AchillesLeftKnee

le_boss wrote:

over the last month or so mine seems to record much lower elevation figures than i would expect.

It uses a barometric altimeter. We've had high pressure over the UK recently. The higher the air pressure, the lower the barometric altitude.

le_boss

ahh, i see.
thanks for the quick reply. was concerned it might be a problem with my device.
never even thought about the weather being a factor :oops:

hatch87

AchillesLeftKnee wrote:

le_boss wrote:

over the last month or so mine seems to record much lower elevation figures than i would expect.

It uses a barometric altimeter. We've had high pressure over the UK recently. The higher the air pressure, the lower the barometric altitude.

Shouldn't make any difference apart from your actual altitude. The amount of elevation will be the same just at a higher/lower points relevant to sea level.

My 500 has been fine this week

anto164

Set some elevation points. I have a few around where i live, so outside my house, 5, and 10 miles down the road too.

IanREmery

I've noticed the elevation/altitude discrepencies on my Garmin 500 over the past month or so yes.

Anto - what do you mean by Set some elevation points?

AchillesLeftKnee

hatch87 wrote:

AchillesLeftKnee wrote:

le_boss wrote:

over the last month or so mine seems to record much lower elevation figures than i would expect.

It uses a barometric altimeter. We've had high pressure over the UK recently. The higher the air pressure, the lower the barometric altitude.

Shouldn't make any difference apart from your actual altitude. The amount of elevation will be the same just at a higher/lower points relevant to sea level.

My 500 has been fine this week

Was assuming, probably wrongly, that this was about elevations at specific points rather than elevation changes which, as you say, should be constant.

le_boss

what i mean is one of my set routes usually shows elevation of 3500ft. however, the past few weeks its only recorded around 2600ft of climbing and a starting point of 400ft, when it should be (and used to be) 600ft.
when i use garmin elevation correction it corrects the figures to somewhere around those i used to get from my 500 (around the 3500ft mark and 600ft starting point).

hatch87

I'm not surprised the starting point has changed, but you shouldn't be losing 900ft of elevation. If your starting point is 200ft lower, then you highest point should be 200ft lower as the change should be constant except in changeable weather.

At the back there is a square of holes which i'm sure is where the barometric altimeter is , make sure they are clear/clean as it might be preventing it from picking up slight variations in pressure

EDIT

Just had a look on Garmin's website http://support.garmin.com/support/searc ... 0000000%7D

It says at the bottom about temp change, are you going out early in the morning or late at night, maybe the 10C + change is affecting it?

dee4life2005

If your garmin resides indoors, and then you go out for a ride this can also cause fluctuations in the elevation data due to the sudden change in temperature at the start of a ride.

I seem to recall (maybe wrongly?) reading somewhere that it should be given time to adjust to the outside temperature before riding, in order to give more accurate height data.

hangeron

As above set elevation point for your house (or wherever you normally start your ride from). Details how to do it are in the Edge 500 manual - but it's easy enough.

You do need to work out the true height as near as dammit of your regular start point though...obviously don't try and take this of the Garmoin or another GPS, but use OS map and interpolate between the contours which are 10m apart or use Earthtools.org and use the Find Elevation above sea level option.

Then when you start your next ride...the GPS initialises...realises it's near your elevation point which is now a known true elevation and zeros itself against that.

There may still be inherent inaccuracies during the ride if the atmospheric pressure rises or falls substantially, but at least the GPS has started off at the correct height.

GiantMike

It seems a poor implementation. I would use GPS to determine height (accurate to within about 50 ft on a nornal day) and then use this known number to calculate baro pressure. Then use a combination of baro pressure and GPS to produce a consolidated altitude figure throughout the ride.

Gizmodo

http://support.garmin.com/support/searc ... 0000000%7D

hangeron

GiantMike wrote:

It seems a poor implementation. I would use GPS to determine height (accurate to within about 50 ft on a nornal day) and then use this known number to calculate baro pressure. Then use a combination of baro pressure and GPS to produce a consolidated altitude figure throughout the ride.

Not sure about the 50ft thing...vertical GPS accuracy is quite a bit less accurate than horizontal accuracy. I would have thought +/-150-200ft would be more like it.