Issues altitude diagram
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@johann-fuehrer said in Issues altitude diagram:
TruFusedAlti. Do we know if Suunto uses the datum elevation or that from satellite triangulation? Or one and then the other?
my5c
Inflation?
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@johann-fuehrer afaik Suunto uses mean sea level. What am I missing ?
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@Fenr1r said in Issues altitude diagram:
@johann-fuehrer said in Issues altitude diagram:
TruFusedAlti. Do we know if Suunto uses the datum elevation or that from satellite triangulation? Or one and then the other?
Dont know. BTW: This was the thread & post I referred to, needed some time to find it again
… https://forum.suunto.com/post/36919 -
@johann-fuehrer Thank you. Very interesting and now my head hurts.
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@Dimitrios-Kanellopoulos said in Issues altitude diagram:
@johann-fuehrer afaik Suunto uses mean sea level. What am I missing ?
The physical model of Earth and the mathematical model of GPS geoid do not match. Not in altitude (and also not in horizontal offsets, but let’s forget this by now). Maps are not based on the GPS geoid but of some agreed MSL - but not to the same over the whole world (https://en.wikipedia.org/wiki/Vertical_datum)
There is lot of stuff about this on the internet, and to what funny results this led like tunnes planned by two different countries which did not met, bridges and other stuff. But the main conclusion is: GPS watches calculate the altitude based on a “ideal” world shape, which does not 100% match. For some parts of the world the altitude calculated match perfect, on others it’s way off (there is some map about the offset here: https://www.esri.com/news/arcuser/0703/geoid1of3.html) . DEM models have correction information based on the location for the GPS calculated values.So for places on earth where the GPS and map data have a “natual” offset, you need an additional correction, if you want to be precise - or live with the altitude profile being OK but have a small or bigger offset.
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@Fenr1r said in Issues altitude diagram:
@johann-fuehrer Thank you. Very interesting and now my head hurts.
I’m sorry for your headaches…
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@johann-fuehrer I have a headache as well
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@johann-fuehrer at the same time I hear / read in other groups of garmin that the DEM is not ok. Am I wrong
? I am asking not to downplay Garmin, I love DEM, but I want to know in practice. At least if it solves issues like @johann-fuehrer has or even @Stefan-Kersting -
@Dimitrios-Kanellopoulos said in Issues altitude diagram:
@johann-fuehrer I have a headache as well
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@johann-fuehrer @Dimitrios-Kanellopoulos
You see, the problem is with the inexact spheroidal shape of our heads vis à vis mean sea level, air pressure and Mondays. Also noses.
@Dimitrios-Kanellopoulos as for @Stefan-Kersting: so Suunto doesn’t use it? Seems like a good case to look at, I agree.
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One of my thoughts was that the problem is that I live 67 degrees north and the gps satellite coverage is not as good as in lower latitudes. The satellites are not as high above the horizon as eg in Central Europe. So the constellation results on lower precision. But the case I described in my last post can’t connect to that issue i think. There must be a missing link between the altitude displayed on the watch and displayed/recalculated in SA
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@Dimitrios-Kanellopoulos said in Issues altitude diagram:
@johann-fuehrer at the same time I hear / read in other groups of garmin that the DEM is not ok. Am I wrong
? I am asking not to downplay Garmin, I love DEM, but I want to know in practice. At least if it solves issues like @johann-fuehrer has or even @Stefan-KerstingI have had the F5 and FR935 and DEM was not really great - as soon as you are in steep areas, the 30m grid is to coarse, even with interpolation. It made my altitude readings worse than without but you have had the choice.
However, I would prefer manual offset possibility in the watch, because here in Vienna I’m always about 8m to high (not really a problem, except you like to know - in watch mode - which altitude you are).
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@johann-fuehrer said in Issues altitude diagram:
here in Vienna I’m always about 8m too high
[Insert own joke here] Forward to Vienna Tourism.
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@Fenr1r said in Issues altitude diagram:
@johann-fuehrer said in Issues altitude diagram:
here in Vienna I’m always about 8m too high
[Insert own joke here] Forward to Vienna Tourism.
Need to take more care of my wording, it seems
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@johann-fuehrer Nah, it’s all very cool.
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When going to work this morning i calibrates manually to 4 masl, some minutes later checking in the office the watch displayed -25 meters.
Now I did a auto calibration, left the watch 15 min with GPS fix. After the auto calibration the altitude fell with 25 meters/minute before it got stable again. The absolute air pressure differs with almost 15 hPA: 1005 on the watch and 1029 at the official weather station.
Something is wrong here…Instagram: https://www.instagram.com/helgelandsbukken/
https://www.instagram.com/suunto_adventures/
IG: Helgelandsbukken, suunto_adventures
Vimeo: vimeo.com/helgelandsbukken
Blogg: https://turblogg.midnattsola.com -
@Stefan-Kersting Hello, if I remember correct, than the Baro reading is no the truth, as long as altitude and temperature ar not correct. This is because the pressure you read and is show is not the ambient pressure but calculated (by reading local pressure and do some maths) . Therefore in a plane on ground you set the local pressure!! by calibrating the altimeter to the real altitude of the airport and this pressure reading then should - but does not always - match you local weather station. Above a certain altitude you switch then by calibrating the altimeter by setting a specific PRESSURE and fly by flight levels which have a more or less undefined altitude due to the changing ambient pressure all over the world (weather i.e.)
Confusing, isn’t it (some more headaches for @Dimitrios-Kanellopoulos and @Fenr1r
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@johann-fuehrer this is the wrong forum to shine with theoretical knowledge. I have a problem with my watch and would like to get some advice or explanation what´s wrong and what I can do with that.
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@Stefan-Kersting may I ask at which location you are?
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@johann-fuehrer as mentioned earlier I am living 67 degrees north. After everything I tested now I think there is something wrong with the barometer sensor…
