David F wrote:
On 12 Feb, 14:10, "John Rowland"
wrote:

Is it hard for GPS to be used to
determine height above sea level?

Mine does (BMW sat-nav), along with north/south etc. Not had much use
for it, but I guess it could be handy for figuring out if you're on a
flyover, or the road undreneath for navigation purposes.

And does it use the height information in conjunction with flyover height
information to work out which road you're on?

My Tomtom has a weakness here. You're heading from Central London to Hanwell
and it gives the correct route, turning off the A4 at one of the junctions
under the M4 elevated section. Then when you get beneath the M4, it suddenly
decides you have wrongly gone on the M4, and gives you a new much longer
route turning off the M4 miles away, with no clue about which A4 junction
you're supposed to use.