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Garmin question

By D-on - Posted on 12 August 2010

I am new to this Garmin caper and have a question about 'elevation'. I have a Garmin 310XT Forerunner and when reviewing a ride the other day I noticed an option at the base of the garmin page that said enable 'elevation corrections'. Now it seems I have been undercooking my hill training ! The new data has almost halved the elevation gains. I know the 310 isn't the most sophisticated piece of equipment but which data set is more accurate ? What is the difference between the two settings ? After reading the posts on The Angry Doctor I may need to set a new training agenda !

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Geek Gear (GPS/Comps/Lights/etc.)

Forerunner vs Edge

Submitted by loki on Thu, 12/08/2010 - 09:50.

I've noticed when browsing rides on connect.garmin.com that the Forerunner device entries show a lot more elevation gain than the Edge devices - for the same ride. eg look up ride profiles for the Angry Doctor and compare.

If you click the little "?" beside Elevation Corrections on the Garmin page it shows the following explanation:

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.

The Forerunner does not have a barometric altimeter whereas the Edge does.

Make sense now?

705

Submitted by FLY on Thu, 12/08/2010 - 14:20.

My 705 regularly shows that my elevation is negative - not sure why as it seems to happen randomly and then the elevation correction fixes it.

Correction is better but not perfect

Submitted by Discodan on Thu, 12/08/2010 - 17:47.

I've seen the same thing with my Forerunner 405. Even using the Elevation Correction there are still some wierd results coming through. If it's using survey data to setd the elevation then I'd imagine it will all depend on where you are (i.e. if they have accurate survey data). Once on the backtracks it would be pretty tough to pick elevation from coordinates only

Satellite Data

Submitted by Rob on Thu, 12/08/2010 - 19:00.

The issue is probably that the Garmin altitude correction uses satellite (radar) elevation data. This is far from accurate. GPS sourced elevation is also far from accurate (+/- 50m isn't it?).

The best source of data is still barometric then. Even if it's not calibrated properly the relative changes should be good unless a big storm front comes over.

they are smaller hills I guess

Submitted by D-on on Sun, 15/08/2010 - 08:51.

Looks like I may need to upgrade to the Garmin Sextant 777 to get a more accurate reading ! Cheers D

Temperature affected

Submitted by hawkeye on Sun, 15/08/2010 - 10:39.

I get my biggest below-sea-level recordings when it's cold. As the day warms up it behaves better. No doubt due to air density. The Edge 500 should be better for this as it tracks temperature, which my 705 doesn't.

The moral of this story is if you want to impress your friends, start that long climb as early as possible in the morning.

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