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My Garmin wants me to tell it what height I'm at so it can calibrate itself. Are the OS spot heights still accurate?
Are the OS spot heights still accurate?
Yes
Just out of curiosity, what do you think could have happened to make them become inaccurate?
what do you think could have happened to make them become inaccurate?
sea level rising due to ice cap melt...glub,glub
sea level rising due to ice cap melt...glub,glub
How would that change the height of the land?
Oh, because I heard that triangulation pillars were now obsolete and that you could 'adopt' one (honestly) - because now all heights were calculated by satellite. Also, I know from conveyancing work that a lot of plans have been re-drawn because surveying is done by satellite now rather than [however they used to do it - theodolite? camera? I don't know].
Thus, I wondered if the spot heights had also been recalculated - by satellite.
Is that really dumb? 😳
How would that change the height of the land?
the height of the land is relative to sea level?
🙂
So the land is floating on the sea and not connected to the seabed?
I see.
the height of the land is relative to sea level?
easier than measuring from the centre of the planet...
the height of the land is relative to sea level?
to its average - it doesn't go up and down with the tide or waves...
Is that really dumb?
Not at all, I was just genuinely interested to know why you thought they may not be accurate.
it doesn't go up and down with the tide or waves..
it does on a Saturday night
Don't forget that you'll need to calibrate it every time you use it if it's a barometric reading. Can't really see why it would need calibrating if it used a GPS altitude (which isn't accurate anyway).
Don't forget that you'll need to calibrate it every time you use it if it's a barometric reading.
Except there is no way to calibrate a garmin edge 305 which uses a barometer for elevation.
[i]Can't really see why it would need calibrating if it used a GPS altitude (which isn't accurate anyway). [/i]
Depends how many satellites it can see. It needs 4 to give height as well as location but I've seen my GPS accurate to within 1m of the quoted heights on OS maps.
How's that work, then?
I suppose it would always be accurate when recording elevation change. Perhaps it takes a "best guess" from its GPS computed altitude.
the height of the land is relative to sea level?
No, it's not. It is measured relative to Ordnance Datum. Historically this used to be an empirical measurement against mean low water spring tide level at Newlyn - but hasn't been for a very long time...
Depends how many satellites it can see. It needs 4 to give height as well as location but I've seen my GPS accurate to within 1m of the quoted heights on OS maps.
That would be luck. I wouldn't bank on much better than 30m accuracy for elevation (based on GPS alone) - hence why many units have a baro function.
It's a Dakota 20. These are the choices on the Altimeter menu:
Auto Calibration - off/on
Barometer Mode - Variable Elevation/Foxed Elevation
Pressure Trending - Save When Power On/Save Always
Plot Type Elevation/Distance - Elevation/Time, Elevation/Distance, Barometric Pressure or Ambient Pressure
Press to Begin Altimeter Calibration - Do you know the Correct Elevation? - Yes or No - Do you want to use the current GPS altitude?
I haven't learnt it all properly yet, I thought I would get to grips with putting a route into it and following that route on a ride before I got into the more occult functions.
I want to know how much climbing I have done on a ride - training for Kielder.
Karin - the best bet is to calibrate it when you get to Kielder. The weather (unsurprisingly) can affect the quoted elevation considerably. I always switch mine on about 20 minutes before setting off (from home). That usually gives it enough time to self calibrate and get used to the weather.
Like I say, I need to learn it more. In the meantime, I will find out what the height is here - from my OS map - and calibrate it when I leave for a ride.
I will use your idea of turning it on 20 mins before I go out. Thanks.