Just wondering about something that bothers me since i've bought my tdv8.

When i change to off road navigation and enter the screen with the car position, the Altitude measurement seems to be always wrong.

I live near the sea and when i'm almost at sea level the GPS reads something like 40m above sea level.

Why? Anybody noticed this?

Does the GPS altitude reading use another baseline? If so which is it?

A few threads about this on Disco3.co.uk.

Basically, it seems the altitude is usually rounded-up to the nearest 50m or so.  The older I get, the more I realise that people confuse wrinkles for wisdom

GPS uses a baseline called the WGS84 ellipsoid.

Without getting overly complicated, what you are observing is most likely down to the difference between ellipsoid height and geoid height. Depending on your global location, this varies by between approximately -105m & +85m.

This should explain it for you http://www.unavco.org/edu_outreach/tutorial/geoidcorr.html

There's a calculator on the page. A GPS in Lisboa, Portugal, should read about 54m at sea level.

Seems correct.
Learned about that in a topography class, but never thought about it regarding the car....

And actually its about correct with the altitude the car reads.