Montana - Different Elevations?

[+Colorado3G's]

Just wondering if others are seeing this too on their Montana's....I'll probably send a bug report to Garmin. The Satellite screen displays a different Elevation than the Elvation Profile and Waypoint screen when saving the waypoint. See my pictures below - 5629 on the Sat Screen and 5651 on the elevation screen(ignore the 1' difference on the waypoint...I moved) Its almost always has about a 25-30' difference.

 

[kb6ooc]

I believe the elevation shown on the SAT page is a purely GPS-calculated elevation. Elsewhere, the elevation is produced using some Garmin proprietary method that combines GPS elevation with the pressure sensor data to come up with an elevation. I live at about 450FT elevation and both are within a few feet of each other - at least at this moment in time.

 

When I was in a plane, the sat page showed some 31,000FT where the other pages showed about 8000FT.

[+dfx]

Barometric pressure is one aspect, the difference between elevation in the WGS84 reference ellipsoid and the elevation in the geoid is another. The elevation shown in most places compensates for that difference.

[yogazoo]

It's not a bug. Sat screen gives you the elevation based on the satellite calculation. Everywhere else it's the barometric pressure calculated elevation. The two are often not identical. You can set up the trip calculator screen to display both the "GPS Elevation" (satellite) and the "Elevation" (barometric) fields.

 

Added: I've also noticed that some fields, in some places display rounded up and some round down. I notice this when I have GPS accuracy field enabled as well as the Satellite dashboard (with the estimated accuracy number) on my Trip Computer page. The two often are 1 foot off. I've seen thig somewhere else too I just can't think of where at the moment.

Edited January 22, 2012 by yogazoo

[+Walts Hunting]

That is well within the accuracy range. If you want to see how much general variance their is just in the elevation by barometric pressure try this: Do a hike that has over 1,000 feet of climb. Reset everything and display the ascend and descend fields. Do the hike out and back on the same trail. When you get back to your starting point you can see as much as 50 feet difference which means you are either the ground has moved 50 feet up or down while you were away or the instrument is off.

[+Colorado3G's]

Thank you everyone for the replies - I do appreciate it and won't report anything as it looks to be normal! Thanks!

[+rchwallace]

As you have found it is normal. Dont think anyone mentioned it but... when you were in the aircraft.... 31000ft was the GPS and Aircraft altitude where as the 8000ft was the "cabin altitude" pressurized.