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Incorrect height readings on Mavic Air and Mavic 2.
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Toedles
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Hi all.
I’ve been helped on the DJI Forum before and wonder if there is someone out there who can help me again.

I own various DJI products, amongst them a Spark, Mavic 2 and a Mavic Air. I’ve noticed that there is a discrepancy on the height shown on the app versus the actual height of the crafts. For example, I’d take off and all is well, after flying for some time I’ll bring the drones towards me (approx 1,8m) but the Go4 app will show -3,0m or any negative number for that matter. This wasn’t always like this. Now, when it changed I honestly don’t recall but it does concern me. I take off on a flat, level sports field and this does not happen with my Spark.

DJI has recommended that I recalibrate my vision system. My front and rear vision system works just fine.

Anyone ever run into a similar issue? 22956F08-488A-45E6-940A-260BC6481102.jpeg FBF54EDD-3297-41CD-BD23-4734EE2A6100.jpeg D5813982-5116-4369-995C-616CA63B83E1.jpeg
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792B05DD-A01D-4000-9F29-78999543BAB6.jpeg
1-9 15:21
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hallmark007
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Your VPS height is correct, you will need to fly above VPS RANGE and check what your barometer is reading, depending what craft your using once VPS comes into range your correct height can be read from this. Bottom right of your telemetry.
1-9 15:45
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Toedles
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hallmark007 Posted at 1-9 15:45
Your VPS height is correct, you will need to fly above VPS RANGE and check what your barometer is reading, depending what craft your using once VPS comes into range your correct height can be read from this. Bottom right of your telemetry.

Thank you for your reply. So, should I discard the “H” readings and fly according to the VPS readings you think?
1-9 15:52
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hallmark007
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Toedles Posted at 1-9 15:52
Thank you for your reply. So, should I discard the “H” readings and fly according to the VPS readings you think?

You will find once your above VPs range that barometer will give correct reading , you can check this as your ascending once Aircraft reaches end of VPS range barometer should be giving correct reading.
Use VPS AT LOW ALTITUDE.
1-9 16:10
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HereForTheBeer
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yes i have with my mavic air.  i have calibrated my vision system but only temporarily helped for me, cleared the issue up for a little while then it slowly and progressively returned.   not really sure what to make of it.  i mean your VPS data isnt that bad, actually fairly close... but i can tell its begining to fall out of calibration..

i have a bit of theory here.. maybe IR system is messing up data...can you do me a test with your drones in low/no light outside in a field..... do a low hover 20 feet up at most (use position GPS for stability) and lower your drone and see how low you get before you get a VPS data for height..then fly back up and do a landing manually  by holding stick down and see how low your drones both get before landing protection kicks in..        my mavic air's IR system is very messy data with low/no light situations.. sometimes it can see the ground as high up as 14 feet over empty dark field then next moment it cant see ground until inches away from it..



  EDIT: disregard the first bit, your VPS data is right, it says meters, i wasnt reading that screenshot correctly...

still can someone test IR data for me?





1-9 16:13
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Toedles
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hallmark007 Posted at 1-9 16:10
You will find once your above VPs range that barometer will give correct reading , you can check this as your ascending once Aircraft reaches end of VPS range barometer should be giving correct reading.
Use VPS AT LOW ALTITUDE.

Okidoki, I’ll have a play around and see what is happening. Thank you.
1-9 16:21
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HereForTheBeer
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Toedles Posted at 1-9 16:21
Okidoki, I’ll have a play around and see what is happening. Thank you.

IMU and Baro both can provide altitude data while flying which can differ from VPS data..  and so that H is the height in relation to take off location, that is its zero point.  
1-9 16:28
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Toedles
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HereForTheBeer Posted at 1-9 16:28
IMU and Baro both can provide altitude data while flying which can differ from VPS data..  and so that H is the height in relation to take off location, that is its zero point.

Alright, makes sense kinda. I still don’t quite understand why the huge discrepancies in basically the same spot. As another user has pointed out, he’s recalibrated all the sensors, issues disappeared for a time and then slowly creeped back.

I’m not quite sure how to go about this.

1-9 16:37
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Toedles
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HereForTheBeer Posted at 1-9 16:13
yes i have with my mavic air.  i have calibrated my vision system but only temporarily helped for me, cleared the issue up for a little while then it slowly and progressively returned.   not really sure what to make of it.  i mean your VPS data isnt that bad, actually fairly close... but i can tell its begining to fall out of calibration..

i have a bit of theory here.. maybe IR system is messing up data...can you do me a test with your drones in low/no light outside in a field..... do a low hover 20 feet up at most (use position GPS for stability) and lower your drone and see how low you get before you get a VPS data for height..then fly back up and do a landing manually  by holding stick down and see how low your drones both get before landing protection kicks in..        my mavic air's IR system is very messy data with low/no light situations.. sometimes it can see the ground as high up as 14 feet over empty dark field then next moment it cant see ground until inches away from it..

I’ll go and experiment with it later in low light conditions. I’ve noticed that both my Mavics don’t read the ground well at all and it’s very easy to literally fly into the ground. This is in broad daylight. I have to be so careful with these 2. I would be flying straight, 1m over the ground and next thing you know you’re sitting at 0,3m, without any stick input from my side, so hence I’ve learnt to lift my drones up much higher.

Interesting though that DJI can’t really give me a definite remedy. Try this, try that, same old.
1-9 16:47
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HereForTheBeer
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Toedles Posted at 1-9 16:37
Alright, makes sense kinda. I still don’t quite understand why the huge discrepancies in basically the same spot. As another user has pointed out, he’s recalibrated all the sensors, issues disappeared for a time and then slowly creeped back.

I’m not quite sure how to go about this.

the vision based system should in theory be more accurate/absolute as its actually measuring the distance with cameras/IR system that are pointing down on both these drones.    the Baro/IMU based system is relative to take off location being zero.. it can vary as baro is measuring pressure of the atmosphere and the IMU is only measuring change in 6 degrees of direction similar to way your iPhone/Android measures your movements and knows your turned your phone a certain way.. same kinda tech(bit over simplified but same concept).. just relative.

and that person was me that your talking about, my VPS/IR system isn't best at measuring distance and i have to recalibrate it ever so often.  because my for example have my drone to match my height, and my VPS thinking im 6.5 feet, i'm actually just under 6 foot.  same thing hover so my camera is lined up with some work i just did on my home, thats little over 12 feet off the ground below it, for some reason VPS thinks its 8 feet up..  then calibrate my dorne using my laptop and do same tests and its more or less correct close enough. says im 5.8 feet tall in same test and the area i worked on is 12 feet up..   but give it time and the accuracy shifts.




1-9 17:08
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HereForTheBeer
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Toedles Posted at 1-9 16:47
I’ll go and experiment with it later in low light conditions. I’ve noticed that both my Mavics don’t read the ground well at all and it’s very easy to literally fly into the ground. This is in broad daylight. I have to be so careful with these 2. I would be flying straight, 1m over the ground and next thing you know you’re sitting at 0,3m, without any stick input from my side, so hence I’ve learnt to lift my drones up much higher.

Interesting though that DJI can’t really give me a definite remedy. Try this, try that, same old.

thanks, that would be awesome if you and anyone else wants to do low light testing.  IR should see the ground form a few feet up reliably even in low light since its immiting its own light.


and mine sometimes does the same thing in broad daylight supposed to stop/slowdown about 2-3 feet up check the ground then land but mine sometimes gets 6-12 inches away then it realizes this and moves up a bit then lands..  but at night the IR system is support wacky with measurements and i have a few times had my mavic air fight some taller weeds and grasss because it ended up not seeing them until it was burying itself in them  same happened when i was trying to land on a sidewalk, for som reason it saw the sidewalk as a obstical last second litterally got maybe 2 inches away from smacking it and blasted off and dirfted into a the hill behind it..couldnt stop it because it didnt know
1-9 17:14
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Toedles
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HereForTheBeer Posted at 1-9 17:08
the vision based system should in theory be more accurate/absolute as its actually measuring the distance with cameras/IR system that are pointing down on both these drones.    the Baro/IMU based system is relative to take off location being zero.. it can vary as baro is measuring pressure of the atmosphere and the IMU is only measuring change in 6 degrees of direction similar to way your iPhone/Android measures your movements and knows your turned your phone a certain way.. same kinda tech(bit over simplified but same concept).. just relative.

and that person was me that your talking about, my VPS/IR system isn't best at measuring distance and i have to recalibrate it ever so often.  because my for example have my drone to match my height, and my VPS thinking im 6.5 feet, i'm actually just under 6 foot.  same thing hover so my camera is lined up with some work i just did on my home, thats little over 12 feet off the ground below it, for some reason VPS thinks its 8 feet up..  then calibrate my dorne using my laptop and do same tests and its more or less correct close enough. says im 5.8 feet tall in same test and the area i worked on is 12 feet up..   but give it time and the accuracy shifts.

Haha, it is you, so sorry, I confused the two replies up. Very informative information, I guess it also doesn’t help much being in Auckland, New Zealand as I can imagine the atmospheric pressures are probably all over the place. I will do those experiments tonight though, might be interesting.
1-9 17:19
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Toedles
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HereForTheBeer Posted at 1-9 17:14
thanks, that would be awesome if you and anyone else wants to do low light testing.  IR should see the ground form a few feet up reliably even in low light since its immiting its own light.

No problem. I’ll give it a try later when the sun starts to go down which is much, much later around 20:30.
1-9 17:27
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HereForTheBeer
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Toedles Posted at 1-9 17:27
No problem. I’ll give it a try later when the sun starts to go down which is much, much later around 20:30.

no worries and no rush!
1-9 17:51
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Toedles
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HereForTheBeer Posted at 1-9 17:14
thanks, that would be awesome if you and anyone else wants to do low light testing.  IR should see the ground form a few feet up reliably even in low light since its immiting its own light.

So, it’s been an interesting evening. Here’s what I have for you.

Mavic 2 Pro: VPS switches on consistently at 10,0m and hits the brakes when landing at 0,8m
Mavic Air: VPS switches on consistently at 4,8m but hits the brakes hard at 0,4m.

Hope this helps a bit.
1-10 01:34
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HereForTheBeer
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Toedles Posted at 1-10 01:34
So, it’s been an interesting evening. Here’s what I have for you.

Mavic 2 Pro: VPS switches on consistently at 10,0m and hits the brakes when landing at 0,8m

Thanks so much.  Last question.  Was this tested in a field in grass/dirt or over pavement?

  Because over pavement 1.3 feet (0.4 meters) is about the distance my Landing protection kicked in Last night testing over my driveway.. but over the grass/dirt it got 6 inches away (visually) before landing protection halted it but the VPS distance showing it was 1.5 ft up still.  Interesting...   

I wonder why my mavic air’s IR system is having a harder time reading distances accurately in lower light.  
1-10 08:14
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Toedles
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HereForTheBeer Posted at 1-10 08:14
Thanks so much.  Last question.  Was this tested in a field in grass/dirt or over pavement?

  Because over pavement 1.3 feet (0.4 meters) is about the distance my Landing protection kicked in Last night testing over my driveway.. but over the grass/dirt it got 6 inches away (visually) before landing protection halted it but the VPS distance showing it was 1.5 ft up still.  Interesting...   

You’re welcome, this was over short grass, cricket pitch.
1-10 10:37
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HereForTheBeer
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Toedles Posted at 1-10 10:37
You’re welcome, this was over short grass, cricket pitch.

yea sounds like more of an isolated issue with my IR system on my Mavic Air not understanding grassy areas in low light.
1-10 11:28
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Toedles
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HereForTheBeer Posted at 1-10 11:28
yea sounds like more of an isolated issue with my IR system on my Mavic Air not understanding grassy areas in low light.

I think it can be quite confusing for those sensors. I mean can you imagine shooting down this IR light to land but oh hang on, a longer piece of grass just came into view in the prop backdraft, we lift, nope, it’s gone, we drop......

It’ll drive me insane too lol.........
1-10 12:05
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aGuyOfGuys
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are you the baby
1-10 12:10
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Toedles
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Excuse me?
1-10 12:18
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aGuyOfGuys
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are you the baby shown in some of the pictures
1-14 11:33
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Toedles
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Yeah mate, I’m the 3 y/o and the old man with the RC, flying the Mavic, is my grandfather. What do you think? LMAO..........
1-14 11:40
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