How does drone calculate altitude ?

[Gorlash]

We took our M2P out to the levees behind Newark Ohlone College, CA, yesterday. I remain amazed at the wonderful quality of the images that we get from it!! What a babe. I'm still shooting in P mode, and almost everything is set to defaults.

I *did* notice an odd thing about the position data from the drone; it would report horizontal position as 0 feet, when it was actually some 20' above the ground and clearly visible to us!
My GPS in my phone was not so confused, and showed our altitude (that is *us* on the ground, not the drone, of course) as being about 10', which was roughly correct since we were sitting on a levee.
I was flying over a large lake out there, and I know that the drone sensors can be mislead by water, but I was doing some of these observations (of horizontal position) specifically when it was above land. I also noticed the same errors when I was shooting a ruined shack out there, and water was nowhere nearby, but it *still* says 0 feet while it is well above ground.

What is the source of this error? Is it something that I can somehow adjust?

 

[Not A Speck Of Cereal]

First off, are you aware that the altitude displayed is AGL (above ground level, or above the Home Point)? It is not an Above Sea Level reading.

But yeah, it should have read a positive non-zero number if it was above the HP.

Note that it can be a minus number too, if you take off, then descend to a point below HP (such as in a ravine).

In answer to your question, the compass is barometric. It is not super, scientifically accurate though.

Chris

 

[Gorlash]

First off, are you aware that the altitude displayed is AGL (above ground level, or above the Home Point)? It is not an Above Sea Level reading.

[...]

Chris

Whoa!!! No, I missed that entirely!! That makes everything make sense now. The levee that we were sitting on was roughly 10 or 15 feet above water level - which itself might not even be sea level, since it is at the end of a long, wandering slough (Mowry Slough).

Okay, that puts everything in perspective, thank you!!

 

[bumper]

-snip-

In answer to your question, the compass is barometric. It is not super, scientifically accurate though.

Chris

I assume you meant to say, "the altimeter is barometric". Compasses will remain magnetic (unless one throws GPS into the equation). GPS altitude is probably the least precise dimension GPS can discern (compared to lat and lon). In manned aircraft, GPS altitude can vary from altimeter reading by a couple of hundred feet either way.

 

[Gorlash]

What I'll try to train myself to do in the future, is... once the the drone has been running for a couple of minutes, make a note of what altitude it is showing before it heads out... that'll give me at least a rough baseline, to interpret the later values that I get.

 

[MaxHam]

I *did* notice an odd thing about the position data from the drone; it would report horizontal position as 0 feet

The horizontal position can be 0 feet while the drone is 1500 ft up in the air - when it is above you.
Horizontal means the distance in the plain/level between drone and homepoint - wherever you set it:
At drone (take off spot) or RC (your position during take off) and has nothing to do with altitude.

Yes - altitude is determined barometric on drones. Like on any upscale GPS device for hikers or similar which have a tiny hole to read barometric pressure.
I didn't know myself until I got into drones but GPS is real bad for altitude reading. It may be off by a lot.

 

[PS01]

This leads me to wonder: we can use drones to measure building height, can't we? But the question is: should we take off right beside the building (as close as possible) or can we take off from anywhere we want? I've always wondered how drones calculate height. From the home point up or from its current location up?

 

[sar104]

The horizontal position can be 0 feet while the drone is 1500 ft up in the air - when it is above you.
Horizontal means the distance in the plain/level between drone and homepoint - wherever you set it:
At drone (take off spot) or RC (your position during take off) and has nothing to do with altitude.

Yes - altitude is determined barometric on drones. Like on any upscale GPS device for hikers or similar which have a tiny hole to read barometric pressure.
I didn't know myself until I got into drones but GPS is real bad for altitude reading. It may be off by a lot.

For relative height measurement over short periods, barometric is more reliable than GPS. For absolute altitude AMSL measurement, GPS is much more accurate than barometric.

 

[Jeff A]

<SNIP>
Yes - altitude is determined barometric on drones. Like on any upscale GPS device for hikers or similar which have a tiny hole to read barometric pressure.
I didn't know myself until I got into drones but GPS is real bad for altitude reading. It may be off by a lot.

If you expect any kind of accuracy at all, you will have to have a way to set the local Barometric pressure. I would be stunned to learn there is actually an altimeter in our drones.

 

[WithTheBirds]

If you expect any kind of accuracy at all, you will have to have a way to set the local Barometric pressure. I would be stunned to learn there is actually an altimeter in our drones.

You are stunned then.

Also have you considered that the barometric pressure at the take off point may be set as a reference when initialising? That would alleviate what it seems might be your concern with respect to pressure changing with location and other atmospheric conditions.