GPS train location and computer control

[tree68]

blue streak 1

There is a further problem in using GPS for air navigation.  Airplanes have to use two different altitudes.  One is indicated altitude which all airplanes fly at. 

Aircraft barometric altimeters are corrected to sea level, as I recall.  

GPS gives altitude with relation to sea level.  Right now my phone's GPS app shows my house at ~200'...  Better be careful when I step outside.

[Overmod]

tree68

GPS gives altitude with relation to sea level.  Right now my phone's GPS app shows my house at ~200'...  Better be careful when I step outside.

The setup in my R-class Mercedes constantly displayed z as "altitude" (naturally, understood with reference to sea level because the vehicle can be assumed to be sitting on terrain almost 100% of the time, no matter how fast you drive).  As I recall, with 7 or 8 satellites indicated in reception (which I might have been reading in the Microsoft GPS program for streets and trips or whatever, using their proprietary dongle) you could watch the 'altitude' display reading down to feet, although I didn't cross-reference it with a true topo map.

[NittanyLion]

I'm skeptical there's a major deviation in altitude readings.

I used to work as an FAA contractor that was involved in ATC systems and it literally never came up.  ADS-B wouldn't even work if that was an issue.

[BaltACD]

NittanyLion

I'm skeptical there's a major deviation in altitude readings.

I used to work as an FAA contractor that was involved in ATC systems and it literally never came up.  ADS-B wouldn't even work if that was an issue.

I have some Garmin VIRB action cameras for recording my on track activities in the race car.  I also can mount them to my Triumph TR-7 to record pleasure drives.

When in the Triumph the starting point and the ending point are the same - however the displayed 'altitude' will vary by 10 to 15 feet.  The camera get their data by recording GPS data.

[tree68]

BaltACD

When in the Triumph the starting point and the ending point are the same - however the displayed 'altitude' will vary by 10 to 15 feet. 

When I was preparing my last post, my phone app GPS was sitting in front of me (and under a metal roof) whilst the displayed altitude varied some 40-50 feet up and down...

I happen to know that my altitude above sea level here at the house is about 200 feet.  There's a benchmark not far from the house.