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Elevation Repeatability

raiderma
over 4 years ago

I did a ride today that brought me to the same point 3 times via different roads in about a 20 minute time period. Weather was stable and dry. My results were:

1) 390'

2) 373'

3) 375'

My partner had an 810 and her results were all within a couple of feet (390', 390' and 392').

The point where we stopped is very close to the 380' line on the topo map

If call the actual altitude 390' (4 out of 6 readings agree) then my 1) is good and 2) and 3) are out to lunch.

Why the 17' difference?

  • 0 over 4 years ago

    Don't worry about it.  Vertical position is less accurate than horizontal position and less relevant.  It doesn't really matter that much if your elevation numbers are not correct.  The only way to know which unit was telling the truth is to actually get a survey of the point in question.  Just because some readings were the same doesn't mean they were right, just consistent.

  • 0 over 4 years ago in reply to Wongataa
    Wongataa said:
    Just because some readings were the same doesn't mean they were right,

    I like that statement because it's true (not after 100 identical readings though).

    Your statement that vertical position is less relevant is purely personal of course; for many it matters, apparently.

  • 0 over 4 years ago in reply to Martin Borsje

    It is true that some people elevation accuracy is of supreme importance but I don't understand why..

  • 0 over 4 years ago

    Because of the change of pressure/temp and cant handle that. Here it is an example, both of the barometers (Fenix3 415.2m and Edge 830  416.0m at the dedicated point) drifted ~10m after the last descent comparing to valid altitude , the green chart is a dual band GPS receiver altitude data, at the dedicated point the official altitude on the ground by DE GEO department is 400.5m, the mobile measured 402.3m in my backpocket, so need to deduct ~1.4m (~400.9m on the ground, so it  is very accurate when my back has clear sky view :) would be more accurate on handlebar for sure)  ,  and 1m from both Garmins because those were on handlebar. 

  • 0 over 4 years ago in reply to Luko79

    If the delta was caused by pressure then I would expect both the 810 and 830 to show similar readings as they both use baro altimeters. Notice I didn't say accuracy I anywhere in my original post because I do not expect a baro altimeter to be accurate. According to Wunderground, pressure remained a steady 30.00" during our ride so ambient pressure can be eliminated as a cause of any variability. 

    I do expect repeatability if I go to the same point with the same atmospheric pressure. XX ambient pressure  should always equal YY altitude.