Yes, it is like that. While barometric method beats GPS one in short term
accuracy and precision, it is vice versa in long term.
But for the most cases, users do not care about absolute altitude nor
about the profile being tilted along timescale. What they are interested in
is the geometry of profile and the smooth lines.
And this is, why the barometric altimeter is a superior method for them.
Dne 19. února 2018 6:36:57 Robert Grant <[email protected]> napsal:
I'll take a stab at precision vs accuracy. High precision: Osmand reports
the same value within a very small range for a reference elevation every
time. If reference is 292 feet, I would consider repeated indications of
262 feet to be very precise, though not correct. High accuracy: Osmand
shows the correct value for the 292 ft reference elevation. If Osmand
reports 292 feet exactly I'd consider that highly accurate. If an hour
later Osmand then shows 414 feet at the same position, that report is not
accurate. If it later shows 210 feet that too is not accurate. If more
readings showed continued variation despite being spot on occasionally, I'd
conclude that the device has low precision.
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On Sun, Feb 18, 2018 at 3:44 PM, Isaac <[email protected]> wrote:
The discrepancy between devices was my fault - I just realized that I had
uninstall the world altitude correction map but the altitude corrections
did not revert at that point. Seems a little strange to me, but the higher
value only reverted after rebooting the device. It now matches the already
corrected value that is output from the Garmin.
The "Bluetooth GPS" app that I use also allows for geoid correction, so it
theoretically can be applied as many as three times if that box is checked
in addition to the osmand and Garmin corrections.
On Sunday, February 18, 2018 at 1:36:12 PM UTC-5, Greg Troxel wrote:
Poutnik <[email protected]> writes:
> For me, it looks like both internal GPS units, in agreement with my
> experience, do not provide geoid correction to the amplitude. Therefore
> is is about 120' lower than the reference, what is about the correction
> value for US region.
The Android specification is to return ellipsoidal height:
https://developer.android.com/reference/android/location/Location.html
and one can get the NMEA also and use either geoid height or GPGGA
(orthometric) height:
https://stackoverflow.com/questions/2791927/how-does-getalti
tude-of-android-gps-location-works#2797026
https://stackoverflow.com/questions/9361870/android-how-to-
get-accurate-altitude
The real question is what's up with the external unit and how that
works. If it's being connected in to replace the internal GPS and
accessed via the same interface, it needs to report ellipsoidal height.
But the fact that it shows the higher (presumably close to correct for
orthometric height) value in satstat on both phones leads me to believe
that the android location/altitude (misnamed) interface is being used to
get the orthometric height from the bluetooth unit. That's the big
mystery.
The other mystery is that one of your phones seems to have the elevation
correction map in OsmAnd and the other does not.
Probably OsmAnd should change the symbol to something other than
mountain, perhaps "EH", to indicate that it's showing ellipsoidal
height, or make it red.
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