Sat nav altitude - how does it work?

[glastoveteran]

Hi all,

Does anyone know how the altitude shown on the nav screen is calculated? Is it an actual altimeter or is just from the map data?

I'm sure recently it's given me two different altitudes for the same bit of road on different days...

I've thought about testing it out next time I'm on top of a multi-storey car park but asking here would be easier!

Thanks

 

[peddy]

it's calculated and not very well by the looks of it... http://gpsinformation.net/main/altitude.htm

 

[AlanJ]

Consumer GPS operates on the assumption that the world is a pefect sphere and makes simple height/surface position calculations accordingly, hence relative inaccuracy and variation. Professional GPS instruments (military, aviation etc) use the geodetic reference system which provides accurate references for the earth surface from which accurate height calculations can be made. Consumer access is limited to the basic reference system as it rare that we need accurate heigh information or indeed accuracy greater than about 10-15 metres for navigation from point to point.
Anyway with Mrs J in the car I don't need GPS - just wish I could reduce the volume and change the voice character..... :rofl: