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Barometer Accuracy
1225 4 2016-1-31
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nigelw
First Officer
Flight distance : 518084 ft
United Kingdom
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Looking through my flight records for my P3P, the altitude shown at the end of each flight shows there's always a discrepency of between 0 & 10 metres between take off & landing heights when landing at the home point.  The worst reading has been 18m higher than take off altitude!

Has anyone else experienced this?  Can you post your landing heights to compare please?  Just a rough idea from a random selection is enough.

All I need is the landing heights, which must be at the original home point.  You can find it in your flight records by pushing the slider across to the right as below...

You can also get it from healthydrones if you've uploaded your flight records.  It's shown as the last known location under the details tab.
Flight record.jpg
Healthy Drones Flight record.jpg
2016-1-31
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aburkefl
First Officer
Flight distance : 78612 ft
United States
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I think the consensus seems to run between ridiculous and hilarious! Sometimes, the altitude numbers don't even seem to be "in the ballpark!"

I thought with three satellites one could calculate the altitude. I have a Garmin GPS (an Edge 810) that I use for bicycling - it *does* use the GPS to calculate both speed and altitude. For whatever reason, however, DJI opted not to use that particular algorithm and they use barometric pressure to calculate the altitude.

One of the math advantages with the DJI approach is that you don't have to know the actual height MSL (Mean Sea Level). No matter where you are, the ground is theoretically a level of zero feet. It does look funny though. If you take off on even a small cliff/hill, you can quickly get a negative value for your altitude. Looks funny until you get used to it.

Art - N4PJ
Leesburg, FL
2016-1-31
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nigelw
First Officer
Flight distance : 518084 ft
United Kingdom
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aburkefl@gmail. Posted at 2016-1-31 12:41
I think the consensus seems to run between ridiculous and hilarious! Sometimes, the altitude numbers ...

I'm pretty sure the Garmin uses map data to calculate the altitude.  Mine is the same (Memory Map).  Without a map loaded, it can't tell me the altitude.  The reason is that altitude is nowhere near as accurate as horizontal positioning from GPS.  Imagine you have 4 satellites but they're all near the horizon...the differences in distance to each satellite is very small as you move upwards, so calculating height can be a hit & miss affair.
2016-1-31
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aburkefl
First Officer
Flight distance : 78612 ft
United States
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nigelw Posted at 2016-1-31 07:48
I'm pretty sure the Garmin uses map data to calculate the altitude.  Mine is the same (Memory Map) ...

You're probably spot on about the calcs. I live in central Florida and we don't have much elevation change here. The highest spot in the state is 345 feet above sea level. The highest place close by is a whopping 330 feet - Sugarloaf Mountain!

I don't generally pay too much attention to the "total elevation change" after a bicycle ride here. It's more important when I ride up in the mountains!
2016-1-31
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Kneepuck
Captain
Flight distance : 275105 ft
United States
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That's why modern aircraft have several ways to determine altitude.  One of the most accurate ones is the radar altimeter.  Barometric pressure can be affected by many things.  I understand nowadays a laser altimeter is often employed.  Supposed to be very accurate. And it should be,  at least far more accurate than simply barometric pressure.
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2016-1-31
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