Height from where?

[Meta4]

I believe that the Phantom gets its altitude information from both the onboard GPS and Barometer (A few high end portable GPS do). The Barometer is also the back up sensor in case you loose the GPS signal, but the barometer is not very reliable because it is subject to air density which is constantly changing due to elevation, high and low pressures in the atmosphere and temperature. Look at a barometric pressure chart for any given day and you will see what I am talking about.

+/- 15 meters 95% of the time is the standard error for GPS altitude. Good enough for my needs. A standalone altimeter doesn't report real time back to the controller.

No .. GPS is fine for horizontal position, but very poor for altitude and commonly out by 100 feet or more in either direction.
This is easily checked with any handheld Garmin any time you are on a boat or by the sea.
That's why DJI get no altitude data from the GPS. It would be so unreliable that it would be useless.
The barometer is accurate to inches and the amount that atmospheric pressure varies during the day is meaningless when your max flight time is 20 minutes.

From Garmin's support page ...
How accurate is the GPS elevation reading?
07/10/2015

GPS heights are based on an ellipsoid (a mathematical representation of the earth's shape), while USGS map elevations are based on a vertical datum tied to the geoid (or what is commonly called mean sea level). Basically, these are two different systems, although they have a relationship that has been modeled.

The main source of error has to do with the arrangement of the satellite configurations during fix determinations. The earth blocks out satellites needed to get a good quality vertical measurement. Once the vertical datum is taken into account, the accuracy permitted by geometry considerations remains less than that of horizontal positions. It is not uncommon for satellite heights to be off from map elevations by +/- 400 ft. Use these values with caution when navigating.

 

[Chris Vedeler]

I suppose it depends in part by how many satellites you have contact with. I have found my iPhone GPS to be fairly accurate with altitude here in Arizona with no clouds, no trees and big blue sky. On the ground with trees or other obstacles the altitude accuracy would probably suffer. With GLONASS added in I would think it may be a little better.

I can understand why you wouldn't want to navigate IFR by GPS altitude in a real airplane, but it is easy for any GPS receiver to get this information and it would be just as easy to transmit the reading to DJI Go. What is the harm as long as there is a disclaimer not to count on it for navigation purposes? If it is so useless why do they have it with a handheld GPS units?

 

[Meta4]

I suppose it depends in part by how many satellites you have contact with.

Read the note from Garmin above. It is useless.
This has nothing to do with number of satellites. It is all to do with spherical geometry.
Often on the deck of a yacht, 1 metre above sea level it will say I am at -100 feet and a minute later it says I am +60 feet. And that is with a clear horizon and max satellites.
GPS is worthless for altitude. Your Iphone probably has a barometer itself or is adding something from cell tower info.
GPS altitude accuracy is +/- a couple of hundred feet
Barometer accuracy is +/- a couple of inches
And that is why DJI don't use GPS data for altitude.

 

[Mal_PV2_Ireland]

I hope far enough he don't end up like this
View attachment 29455

I'm amazed someone hasn't really messed with this drawing and made me snot Guinness out of my nose yet

 

[43k]

I hope far enough he don't end up like this
View attachment 29455

You mean "she", no?

Look out for those flying blenders!

 

[43k]

That's better.

 

[dirkclod]

That's better.