Garmin 500 altitude accuracy

ravenvrider

I bought a Garmin 500 last week, i am struggling to believe in anything it says regarding altitude, i have used it for 6 of my commutes home, on exactly the same route every ride, it registered these heights;
554, 568, 515, 554, 584, 499 feet.
When i used my phone, it was generally about 350feet every day (galaxy note 3)

I am unsure if there is something i should do to the device (set up) it is connected to garmin connect everyday and i have updated software etc.

Is this a faulty unit or is there something i can try, do you guys with them have these kind of differences in your results.

Thanks for any help.

Grill

The 500 uses a barometric pressure sensor, so it's far more accurate than your phone. Still not immune to fluctuation, but you can alleviate some of it by setting a base altitude.

ravenvrider

Yes i read several reviews and was expecting it to be different to my phone but i was expecting it to at least be consistent to within a few feet daily not have 85 feet difference.

I was also aware due to its supposed accuracy that it should have elevation corrections disabled which it was, i have just enabled them for todays ride and it has come back at 367 feet which is 15 feet higher than my phone normally comes in with.

Having just read DCrainmakers review of the edge 1000 with an altitude test up a 5000ft climb that was 20ft out which over 5000 ft is highly acceptable, having a variance of 85ft on a supposed 550ft of climbing (which is possibly more like 360 ofdd) seems seriously bad.

wongataa

GPS altitude is not very accurate. Barometric altitude can be very accurate provided it is calibrated and any pressure changes due to weather are compensated for.

marcusjb

ravenvrider wrote:

Yes i read several reviews and was expecting it to be different to my phone but i was expecting it to at least be consistent to within a few feet daily not have 85 feet difference.

As per other comments, did you calibrate it before each trip? Air pressure will vary considerably over a 5 day period and calibrating your unit before each ride will improve the readings you are getting.

I have an 800 and a 510 and both give pretty consistent readings on regular circuits, provided I calibrate as I set off.

rolf_f

For commuting I use a Bryton 20 without a barometer. The elevation for each commute has minimal recorded variation (what there is is probably down to slight variations in the exact pathway of the route) because it is entirely defined by the digital terrain map used by the site the route is uploaded to.

Ultimately, this will always be an underestimation (but probably not by anything significant) but it should always be consistent. And that's really what matters. It doesn't matter if you measure elevation in feet or carrots - consistency is what matters and you don't really get that with the barometers. If there were no barometers in GPS units, we wouldn't end up with 25% discrepancies between different riders on the same routes.

antfly

You only have to set your altitude once for home and work and when you press the start button at those places it auto-calibrates and that makes it a lot more accurate, if you haven't done it yet..having said that the barometer/altimeter on the edge 800 seems to be a lot better.
Barometers are far superior to GPS for accurate altitude, they measure every foot you go up and down but if you only want an estimate use elevation corrections.

ravenvrider

I have not calibrated it yet but looking at the data it is spot on...I set off a 10 ft and home is 20 ft and it has been consistent on those points if just seem the cumulative amount is out.

cmhill79

I've seen a garmin edge rise 20 feet before and that was while I was having a coffee...

ai_1

GPS gives an absolute measurement but vertical accuracy on commercial GPS is poor.
Barometric altimeters give far more accurate measurement of changes in altitude but as atmospheric pressure is not constant, the offset must be corrected each time you use them if you want the actual altitude to be correct.

If you're looking at figures for how much climbing or descending you do on a ride then there's a much more important factor to consider: There is no right answer!
The value you get for ascent or descent will be completely dependent on how you measure it. If you draw straight lines between the highest and lowest points and ignore all the undulations in between you'll get one answer. If you include "medium sized" undulations you'll get a bigger answer. If you include every ripple in the road surface you'll get a much bigger answer again. I'm not just being pedantic, this is a very real issue and I'm sure the main cause of confusion with comaprisons between different results for the same terrain. The same issue occurs for distance travelled too but because the distances are much greater and we can follow a fairly smooth course on the road the impact is tiny by comparison.

owenlars

With a barometric altimeter every 1 millibar change in pressure changes the barometric altimeter reading by 28 feet. So if atmospheric pressure is 1000 millibars on a Monday when you set out from home and your unit reads 100 feet above sea level then on Tuesday when you set off atmospheric pressure has increased to 1001 millibars your unit will read 72 feet above sea level.

Clearly your home has not just sunk 28 feet! The actual amount of climbing and descending your unit calculates will, of course, be the same on both days provided atmospheric pressure does not change during your ride.

Pilots have constantly to change their altimeter settings to take atmospheric pressure into account and whether they are requiring their height above sea level (altitude) or above the local ground level (height).

chris_bass

I find when the weather is bad mine is terrible.

if it is windy it usually adds loads of climb and if its very wet it just stops altogether. I've kind of given up on it now and just ignore it.

adr82

Chris Bass wrote:

I've kind of given up on it now and just ignore it.

This is the correct answer. Who cares if you get your total altitude correct to the nearest 100ft, never mind 10ft? It doesn't change how much climbing you actually did, does it??

Rodders30

My 510 is about 1000ft out. Perhaps I should look into calibrating it....lol

ai_1

Rodders30 wrote:

My 510 is about 1000ft out. Perhaps I should look into calibrating it....lol

....and put it in metres!

bobbydazzla

My Edge 500 is miles out on altitude. Last weekend I rode with a friend who also has an Edge 500 - mine showed 6700ft, his showed 6000 ft. The route was definitely closer to 6000ft.

Yesterday I rode a Sportive. Organisers claim 7500ft of climbing, my Garmin shows 8700ft, other Garmin users who did the ride show roughly 7500ft and if I use elevation correction in Strava / Connect it shows 6800ft.

So why is my unit so far out compared to others and what can I do to correct it ? If I set the altitude on my unit from a fixed point (probably home), do I need to do this before every ride or does it store that point for future reference ?

antfly

You only have to set your altitude once and every time you press start from there it calibrates, it won't be as accurate without calibrating at the start. The Edge 800 has a much better altimeter, though.

ravenvrider

Even calibrated my unit still has wide discrepancy's on my daily commute, so wind up hitting the enable elevation correction button, which at least seems to be much closer to what i believe the actual figure to be.

So from my perspective garmisn altitude certainly on the 500 is way too unreliable to bother with.

bobbydazzla

antfly wrote:

You only have to set your altitude once and every time you press start from there it calibrates, it won't be as accurate without calibrating at the start. The Edge 800 has a much better altimeter, though.

Cheers, have calibrated my Garmin to home. The Garmin had my altitude at -18 meters, whereas the Daftlogic altitude calculator website had a more accurate +49 metres.

And how accurate is the elevation correction on Strava / Connect supposed to be ? Yesterday's Sportive had total climbing listed at 7789ft, but when I correct my ride it's only 6800ft. Surely the organisers can't be 1000ft out ? It's a well established event with a similar route each year....

wongataa

[quote="bobbydazzla"And how accurate is the elevation correction on Strava / Connect supposed to be ? Yesterday's Sportive had total climbing listed at 7789ft, but when I correct my ride it's only 6800ft. Surely the organisers can't be 1000ft out ? It's a well established event with a similar route each year....[/quote]
Altitude correction on websites uses data from satellite/space shuttle mapping missions. The accuracy is not always that good. There is quite a gap between data points reducing measurement accuracy of smaller features and missing data due to such things as cloud cover doesn't help.