Garmin Connect - Elevation

meanredspider

I know it's often discussed but it's so obviously wrong even using its own data

My ride home http://connect.garmin.com/activity/85375045 on Friday has two peaks (as measure by the Garmin):

1st at 347ft (OS level 331ft)
2nd around 618ft (OS level 616ft)

and the low points between at more-or-less sea-level or just above.
There's also plenty of ups-and-downs on the whole ride.

And total elevation gain according to Connect?

907ft

a figure spookily close to taking the two lowest points and subtracting the two highest points.

So clearly wrong. Garmin Training Centre comes up with 1200ft

How come Connect manages to get it so wrong? Disappointing.

notsoblue

If your Garmin doesn't have a baromatric altimiter, the GPS height readings can be quite inaccurate. What you could do in your case is to enable "Elevation Corrections" for your Garmin routes.

Garmin Site wrote:

What are Elevation Corrections?
Elevation Corrections cross reference the horizontal position (latitude/longitude) provided by the GPS with elevation data that has been acquired by professional surveys. When corrections to elevation data are made, each trackpoint of your activity now contains the elevation from the web service, not the elevation provided by your GPS device.
Garmin Connect selectively applies corrections to depict a more realistic representation of your elevation experience. Activities recorded from devices without a barometric altimeter are enabled with Elevation Corrections by default. Alternatively, activities recorded by devices with a barometric altimeter generally contain accurate elevation data and therefore Elevation Corrections are disabled by default. For those users who are familiar with the MotionBased Gravity service, this is the same service.

That might make a difference?

meanredspider

notsoblue wrote:

If your Garmin doesn't have a baromatric altimiter, the GPS height readings can be quite inaccurate. What you could do in your case is to enable "Elevation Corrections" for your Garmin routes.

That might make a difference?

But the heights are pretty close to accurate (347 vs 331 (5%) and 618 vs 616 (0.5%)) - it's the calculation that's wrong from these figures

daviesee

I notice from your link that you have "Elevation Corrections" disabled.

Give it a try, it only involves ticking a box. It may retain the correct heights that you do have but add in additional information. I know that it makes a big difference to the results from my 705.

uphillstruggle

Don't know how/why but the Garmin Forerunner I use for running seems far more reliable in terms of the height gained and calories burnt than my 500?

No idea why that should be.

Also not sure why there is such a large discrepancy between Connect and for example Ride with GPS sites in terms of calories burnt.

If the figures on Connect are to be believed it is barely worth me getting on the bike- 20mile hilly commute av 17ish mph = 550 calories?

Bloody hard way to burn off a mars bar!

meanredspider

daviesee wrote:

I notice from your link that you have "Elevation Corrections" disabled.

Give it a try, it only involves ticking a box. It may retain the correct heights that you do have but add in additional information. I know that it makes a big difference to the results from my 705.

Yup - though I guess you are missing my point.

From the elevation chart that Garmin Connect generates in that link, it's clear that I've climbed more than 907ft. How does Connect interpret the figures that generate that graph and come up with climbing that's less than that graph shows?

If I enable elevation correction, I get a different graph (the peak elevation actually gets more inaccurate and the lowest point in my ride become 33ft BELOW sea level (I don't remember taking a dip in the Beauly Firth)). I do get a 1029ft of climbing but if I dip below the sea I'd expect to.

My point is, the graph does match the figures calculated from the same data.

antfly

uphillstruggle wrote:

Don't know how/why but the Garmin Forerunner I use for running seems far more reliable in terms of the height gained and calories burnt than my 500?

No idea why that should be.

Also not sure why there is such a large discrepancy between Connect and for example Ride with GPS sites in terms of calories burnt.

If the figures on Connect are to be believed it is barely worth me getting on the bike- 20mile hilly commute av 17ish mph = 550 calories?

Bloody hard way to burn off a mars bar!

There is no way it will be, at least not if you have your home elevation set on the 500 and you have the latest firmware. GPS alone isn't very good for altitude. I have had a load of Garmins and the 500 is the most reliable by a long way.

daviesee

meanredspider wrote:

daviesee wrote:

I notice from your link that you have "Elevation Corrections" disabled.

Give it a try, it only involves ticking a box. It may retain the correct heights that you do have but add in additional information. I know that it makes a big difference to the results from my 705.

Yup - though I guess you are missing my point.

I am not sure that I do miss your point. There are only really 2 climbs shown on the graph and they add up to 907 feet so that would make sense - to me but maybe I am missing the point.

Going subsea is a little strange I agree but I don't take these figures too seriously. Especially the calories. I have done some outstanding rides if they were, 6860 on one run! :shock:

meanredspider

daviesee wrote:

I am not sure that I do miss your point. There are only really 2 climbs shown on the graph and they add up to 907 feet so that would make sense - to me but maybe I am missing the point.
:

There are two obvious climbs but loads of "mini" climbs & dips - why should it decide to include the big ones and ignore the small ones? Else, you might as well take the highest point and subtract the lowest point and call that the elevation gain.

I do ignore the calories completely or, if pressed, take 60% as a rough guideline.