Height issue

[Mavic-Max]

Hi folks. Any ideas why my controller is reading zero height when my Mavic air 2 is around 4m above ground level. I am standing on the same spot I hand launched from so I expected the reading to be either 4m or 2.5m to take in the fact that it was 1.5m above ground when it launched. See screenshot. Any ideas much appreciated.

 

[Pappy]

I think it's a Fly app bug as others have reported this as well.

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[Rich QR]

The height displayed on your drone is measured relative to your launch point. It's not measured relative to the ground level unless you launched from the ground. Even then, it's still just height relative to your launch point, not relative to the ground below the drone.

edit: Reading your original post more carefully, it seems the altimeter reading has changed by a few meters during the flight. This may be because the barometric pressure changed, and/or temperature changed. If it consistently happens in the same direction, I wonder if it's due to the barometric sensor warming up during flight due to electrical heating of the sensor or nearby circuitry as the drone is flying?

Anyway, it shows you that the altimeter can't be trusted down to the last meter. That's typical of altimeters.

 

[Meta4]

Any ideas why my controller is reading zero height when my Mavic air 2 is around 4m above ground level.

It's common and normal for the displayed altitude to be a couple of metres out over the duration of a drone flight.
It's just what happens with the barometric sensor that is used.

 

[Mavic-Max]

The height displayed on your drone is measured relative to your launch point. It's not measured relative to the ground level unless you launched from the ground. Even then, it's still just height relative to your launch point, not relative to the ground below the drone.

edit: Reading your original post more carefully, it seems the altimeter reading has changed by a few meters during the flight. This may be because the barometric pressure changed, and/or temperature changed. If it consistently happens in the same direction, I wonder if it's due to the barometric sensor warming up during flight due to electrical heating of the sensor or nearby circuitry as the drone is flying?

Anyway, it shows you that the altimeter can't be trusted down to the last meter. That's typical of altimeters.

Hi. You are bang on with the temperature theory. So I’m getting in some practice for my A2 CofC exam and need to complete 4 hours of flights. I used all three batteries in succession giving me almost 1 1/2 hours of air time. The weather was cool but the constant use will have warmed up the drone. I noticed the height error at the end of the third battery. Today is a new day so with a cool drone and cool battery the height reading is working correctly.

 

[Mavic-Max]

I think it's a Fly app bug as others have reported this as well.

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I also had a minus height reading as did the guy in the video.

 

[Mavic-Max]

It's common and normal for the displayed altitude to be a couple of metres out over the duration of a drone flight.
It's just what happens with the barometric sensor that is used.

I’m thinking it’s to do with the internal temperature of the drone. See my other reply.

 

[old man mavic]

@Mavic-Max ,as with many of the displays ,that show on the App screen ,ie speed, height ,distance etc ,they are not cast in tablets of stone ,and should not be judged as such ,they add to the flight experience ,but in reality they are not as accurate as people think due to the way they work

 

[Meta4]

@Mavic-Max ,as with many of the displays ,that show on the App screen ,ie speed, height ,distance etc ,they are not cast in tablets of stone ,and should not be judged as such ,they add to the flight experience ,but in reality they are not as accurate as people think due to the way they work

Actually, speed and distance are derived from GPS data and should be very accurate.

 

[Meta4]

I think it's a Fly app bug as others have reported this as well.

It has nothing to do with the app and the video guy has no idea what he's talking about.
It's been noted with all DJI drones going back >6 years.
You would probably also see the same in real planes that also use a barometric sensor to provide altitude data.

Just do what real pilots do and don't rely on the altitude data to be accurate to the last metre.

 

[Meta4]

I’m thinking it’s to do with the internal temperature of the drone. See my other reply.

If it was temperature related you wouldn't have some users seeing + while others see negative differences.

 

[SkyeHigh]

If it was temperature related you wouldn't have some users seeing + while others see negative differences.

Absolutely. The pressure sensor has real-time internal temperature compensation with every sensor calibrated during manufacture to provide an accuracy of +/- 1-metre from 0C to 65C. They do not require a ‘warm-up’ period and can produce accurate, valid data within 25ms of power on.

Full-size aircraft pressure sensors operate on the same principle but are more complex and require greater temperature compensation due to the requirement of a very wide operating temperature range.

The sensors used in drones are defined by the manufacturer (usually Bosch) as for ‘consumer use’ only.

 

[WJbdB]

A very accurate GPS position with the gear we´ve got is on it´s best only 3-5meters off. Usually within 10meters.