COMAND NTG2.5 - Altitude

[markjay]

I noticed that the Altitude on my COMAND NTG2.5 is showing as -200 to -400 ft.

Driving around London, this seems unlikely to be correct.

I wonder if the Altitude figure is simply calculated from the satellites triangulation, or is there a separate Altimeter in the head unit or elsewhere in the car?

 

[Ted]

I always thought it was from topographical data embedded in the map - if you know where you are, the map also contains height data.

 

[markjay]

I always thought it was from topographical data embedded in the map - if you know where you are, the map also contains height data.

Interesting - possible, though this scenario does not explain why the location data is correct but the altitude is not...

 

[markmifsud]

Sat nav's get the altitude from GPS triangulation.

 

[camerafodder]

GPS altitude is notoriously unreliable. Driving amongst high rise buildings will increase the error factor as the number of low angle visible satellites required to triangulate an accurate vertical position is higher than for a horizontal position. IIRC.

 

[markjay]

Seems to have settled now.... today it was correctly showing zero.