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Varying Heights

 
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FrequentFlyer
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Joined: Jun 12, 2006
Posts: 959
Location: London

PostPosted: Thu Jul 31, 2014 7:02 pm    Post subject: Varying Heights Reply with quote

While out walking today, I placed my A12 on top of a local Trig Point
The local OS map has it at 245 Mtrs
My A12 Barometer Height showed 238 Mtrs (Hot day!)
Switching to GPS mode, showed 244 Mtrs.

Not sure what you can glean from all this !? Just use GPS ?
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dales
Frequent Visitor


Joined: May 04, 2008
Posts: 737
Location: Knaresborough, North Yorkshire.

PostPosted: Fri Aug 01, 2014 12:49 am    Post subject: Reply with quote

What I can gather from the Garmin wiki site, is that a GPS is good at calculating horizontal distances, but much less accurate at calculating vertical height. So GPS elevation is probably OK at a break stop where the calculations have had time to average out, but not quite as accurate on the march uphill.

In contrast, with the altimeter set to Barometric, then the Garmin unit will start with the known elevation as input by the user at calibration time, and will trend this towards GPS elevation during usage. (Obviously nasty weather changes will inflence these readings).

Finally, if you select a point on the map and click through, you will get the DEM elevation ie the height per the map and its digital interpolation thereof.

Take your pick ! Perhaps use the GPS or Map (DEM) elevation, but not Barometer, as you say !!

Dales
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nuvi 2599LMT-D, oregon 700, basecamp, memory-map.
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dales
Frequent Visitor


Joined: May 04, 2008
Posts: 737
Location: Knaresborough, North Yorkshire.

PostPosted: Fri Aug 01, 2014 1:11 am    Post subject: Reply with quote

What I can gather from the Garmin wiki site, is that a GPS is good at calculating horizontal distances, but much less accurate at calculating vertical height. So GPS elevation is probably OK at a break stop where the calculations have had time to average out, but not quite as accurate on the march uphill.

In contrast, with the altimeter set to Barometric, then the Garmin unit will start with the known elevation as input by the user at calibration time, and will adjust this elevation for air pressure changes during usage. (Obviously nasty weather changes will inflence these readings).

Finally, if you select a point on the map and click through, you will get the DEM elevation ie the height per the map and its digital interpolation thereof.

Take your pick ! Perhaps use the GPS or Map (DEM) elevation, but not Barometer, as you say !!

Dales
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nuvi 2599LMT-D, oregon 700, basecamp, memory-map.
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