Calibration of Altimeter

[Neville MADDEN]

Good morning,  I have OSM And+ with the latest update on a Lenovo Idea Pad Pro Tablet.  On a recent trip to India the altimeter seems to be reading about 50m below known altitudes.  (All Indian Railway stations have their Reduced Level (RL) on the station approach sign).  Is there any way I can re-calibrate and adjust the altimeter?

Thanks

Neville

Queensland

Australia

[Greg Troxel]

GNSS receivers do not actually have an "altimeter". They compute a
position, which includes "height above ellipsoid", often written h.
Then, they convert this, using a "geoid model", to "height above geoid",
often written H. Generally, H corresonds to what people mean when they
say "altitude above mean sea level". (I say "what they mean" because
really understanding height is tremendously complicated.)

In OsmAnd, there is a data file "World Altitude Corrections", that if
you download, you should see heights/elevations displayed as H. If you
don't have that, you get h. For reasons that are unclear to me, this is
marked Android only.

India has pretty high geoid separations -- the difference between geoid
and ellipsoid, written N. It looks like -68m at Mumbai from a quick
look. So this could explain your displayed height values.

If anyone understands what happens on iOS, please share. It's
possible that a model built in to iOS is used.

GNSS receivers typically have builtin models, but also typically they
are extremely poor. For example around me the real value is roughly
-29m and the models say -33m. Most programs that use GNSS output (on
android or normal computers) will back out the receivers model. NMEA
reports H and N, and then one can compute h, which avoids the terrible
model. You can then apply a better model. Really - it's that messy.

[Max1234 Ita]

Hi, try checking if you have installed the "World altitude correction" package; If you have it, remove it, if not, install it. (/// -> Maps and resources -> 

That package is used by OsmAnd to provide a more correct altitude estimation but the behaviour actually depends onwhat equipment is present in the device, as some receivers automatically do that correction (an additional "correction" would be applied, leading to wrong results)

HTH,

Max

[*Hobbit*]

As with many other OsmAnd files and map data, you can fetch

https://download.osmand.net/download.php?file=World_altitude_correction_WW15MGH.extra.zip

and unzip it into wherever your other data files are, and OSMAnd
should just pick it up.

_H*

[danilo baggini]

Le correzioni complicate sono una cosa. Quello che evidenzia il richiedente è  un'altra cosa. Anche io SEMPRE su un dispositivo ho 60 metri di più.  Ed è un ERRORE fisso di Osmand su QUEL dispositivo. Sarebbe necessario avere una taratura MANUALE per dire a Osmand di indicare 60 metri in meno SEMPRE.

--
You received this message because you are subscribed to the Google Groups "OsmAnd" group.
To unsubscribe from this group and stop receiving emails from it, send an email to osmand+un...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/osmand/CABZJgDEhgX%3DM%2Bv_9KM0BH140T-CdEC4kQ8f-42caDc0%3DowdCYQ%40mail.gmail.com.