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DEM vs GPS Calib

In a nutshell, could someone please explain the difference and the benefits of each altimeter calibration method? I only used to have the option of GPS with previous watch.

Thanks,

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Seren over 6 years ago +5

DEM uses the elevation model built into the map. It gets a 2d positional fix then gets the elevation for that position from the model. Advantage is potentially most accurate Disadvantages include reliance…
ted360 over 6 years ago in reply to Former Member +3 suggested

Hello, I was wondering which map is being used to determine elevation. Is it the Worldwide DEM, topo active or some other local, more accurate topo map (if all are selected)... Cheers!

All Replies

0 Seren over 6 years ago

DEM uses the elevation model built into the map. It gets a 2d positional fix then gets the elevation for that position from the model. Advantage is potentially most accurate Disadvantages include reliance on an accurate 2d fix esp important on steep terrain for obvious reason, also sometimes model doesn't match terrain well.

GPS uses the vertical component of the 3d fix. Advantage is no reliance on map model, Disadvantage is often less accurate

0 TomaekThompson over 6 years ago

Thanks for the explanation Halldrine. All things considered, is there consensus which setting is better for the average runner? Or perhaps for a) a road/city runner or b) the a trails/hills runner?

0 Dr Phil over 6 years ago

It all depends how bothered you are about the accuracy/precision of your data. I don't much care as long the elevation gain/loss is pretty evenly matched on an out and return run, or at least realistic for an A to B run. I also don't care if my altitude is a few metres below sea level when running down the beach. For me it's all about the elevation gain/loss.

0 Former Member over 6 years ago

It depends what you're after. DEM gives you the most stable elevation graph overall as the calibration points are fixed. On other hand especially on my location the DEM used by garmin is +10m off compared to Google for example which based on long time GPS average is more close. But GPS has more variety so I cannot see it as a good calibration source on the go.

If you use altimeter to calculate real time data (Appbuilder for example) like grade adjusted pace, power etc. you might want to to turn calibration off or only calibrate at start. You may not want corrections middle of the data calculation as realtime elevation change is your #1 concern.

0 chatlow over 6 years ago

thanks for explaining the difference and sorry for the late reply! I only tend to calibrate once in a while as I'm usually using GPS during an activity once, twice a week minimum, so my altitude never gets too far off, but when it does I will go with DEM

+1 ted360 over 6 years ago in reply to Former Member

Hello, I was wondering which map is being used to determine elevation. Is it the Worldwide DEM, topo active or some other local, more accurate topo map (if all are selected)... Cheers!

0 zippy8500 over 6 years ago in reply to ted360

ive had really good experience with using the DEM method and would advise using this as opposed to the GPS method , see my results in this video over a 4000ft climbOn Ben Nevis in the UK

https://youtu.be/nmekrTmxNPQ