/ Phone gps and height data

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Flinticus - on 13 Nov 2017
I use Viewranger on a Samsung Galaxy 5.

Where does the height data come from?
ianstevens - on 13 Nov 2017
In reply to Flinticus:

The GPS chip in your phone.
captain paranoia - on 13 Nov 2017
In reply to ianstevens:

That's the most likely source. But some mapping apps allow you to use a DEM terrain database, which it interrogates, using the lat/long. I use this feature of OruxMaps, using the SRTM DEM database. I can display both DEM and GPS, and it's interesting to compare the two values.

The DEM database is 'only' a few hundred megabytes...
Flinticus - on 13 Nov 2017
In reply to ianstevens:

I should say 'how is the height calculated?'

Is it an average of signals from various gps satellites or...
captain paranoia - on 13 Nov 2017
In reply to Flinticus:

It comes out of the position fix solution, just like the lat/long (essentially, 3D trialateration), calculated from the differential time of arrival of the satellite signals.

http://gisgeography.com/trilateration-triangulation-gps/

Yes, it's a weighted average, with the particulars of the weighting scheme generally determined by the receiver manufacturer, but based on a number of metrics such as signal strength and elevation.
subtle on 13 Nov 2017
In reply to Flinticus:

> I should say 'how is the height calculated?'

> Is it an average of signals from various gps satellites or...

Wizardry - long ago the witches and wizards managed to work out how to calculate what height they were at and now they sell this technology to phone manufacturers

The wizarding community are amongst the richest in the world.
captain paranoia - on 13 Nov 2017
In reply to subtle:

> The wizarding community are amongst the richest in the world.

I think that's just JK Rowling...
ianstevens - on 14 Nov 2017
In reply to captain paranoia:
Nice link - well explained. Although it does use the phrase "GPS System" - ARGGH!

Going back to the OP, as far as I know Viewranger mapping doesn't include DEM data as standard and uses the GPS data. Not to sure about the OS equivalent, but I would reckon that's the same to keep downloads smaller.
Post edited at 15:05
ChrisBrooke - on 14 Nov 2017
In reply to ianstevens:

If there's one thing I can't stand it's tautology that I don't like.
captain paranoia - on 14 Nov 2017
In reply to ianstevens:

> as far as I know Viewranger mapping doesn't include DEM data as standard

Viewranger must have access to the DEM data, since it uses it for 3D presentation (or maybe only the desktop version does?). Whether it allows this data set to be interrogated to give the DEM elevation for cursor position, rather than GNSS elevation, I don't know.

OruxMaps uses DEM to allow 3D presentation of the map, and to give the DEM elevation when navigating.
deepsoup - on 14 Nov 2017
In reply to ChrisBrooke:
The first rule of tautology club is the first rule of tautology club.
https://xkcd.com/703/
richard_hopkins - on 14 Nov 2017
In reply to ianstevens:

The Viewranger maps based on Open Streetmap do include a DEM. I don't know what its resolution is though. Perhaps it is only included at some higher levels of zoom. You can see this by moving the cursor around the screen and it reads out the height at that point.

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