To test if an update of the Home point (Mini 4 Pro and RC2) could be of help when going hiking uphill, I carried out a test (at the same time I carried out a test of both ActiveTrack Manual and Parallell - that both were successful).

What I found is that the distance to the Home point updates, but not the distance to the ground.  To achieve a correct distance to the ground, I have to land and relaunch the drone to get a proper reading of the height from ground.

This means that for me, now having upgraded my drone to C1, I can go pass the 120m limit (since I am allowed to fly 120m above the ground - irrespectively from where I took off), as this is easier than landing the drone to get correct readings.

My question is; is this an error?  Should the distance from the ground also update when you update the Home Point?

You can see my video here, and at 3:02:20 you can see the Home Point being updated and that the distance to the Home Point is 0m, but the height difference is still the same.

My question is; is this an error?  Should the distance from the ground also update when you update the Home Point?

No, this is not a bug, it should be like this. Only the drone coordinate is updated, not the altitude.

Serg SSA Posted at 9-6 14:01
My question is; is this an error?  Should the distance from the ground also update when you update the Home Point?

No, this is not a bug, it should be like this. Only the drone coordinate is updated, not the altitude.

I suspected that, I just hope this will change later.  In the meantime, I will just have to raise the max height when doing hiking in the mountains :-).

fgange57 Posted at 9-7 00:28
I suspected that, I just hope this will change later.  In the meantime, I will just have to raise the max height when doing hiking in the mountains :-).

"I suspected that, I just hope this will change later.
"

I suspect there is very little chance of that happening, with regards to height all my drones behave this way can't remember about distance.

Sean-bumble-bee Posted at 9-7 00:51
"I suspected that, I just hope this will change later.
"

A good thing I have upgraded my drone to C1 then :-), because then I'll just adjust the max height as said.

Thank you for testing, now i can keep that in mind if i go to the mountains.

TheLittle Posted at 9-7 02:44
Thank you for testing, now i can keep that in mind if i go to the mountains.

DJI can unlock the altitude above 500m on request for your specific drone if you justify the need. I have a friend who lives in the mountains and he did this, flies up several km.

fgange57 Posted at 9-7 00:28
I suspected that, I just hope this will change later.  In the meantime, I will just have to raise the max height when doing hiking in the mountains :-).

The homepoint and zero height are unrelated.
The zero height comes from the IMU at startup.
The homepoint has no height, just lat/long data and comes from the GPS when full reception is achieved.

Altitude is always relative to the Home Point.  This is the only practical way for it to work.  Providing real-time altitude AGL would require a massive onboard terrain database, a full-time internet connection to access a cloud-based terrain database, or an active radar or LIDAR system.

Serg SSA Posted at 9-7 02:53
DJI can unlock the altitude above 500m on request for your specific drone if you justify the need. I have a friend who lives in the mountains and he did this, flies up several km.

That is exactly what I achieve by upgrading to C1

fgange57 Posted at 9-7 11:35
That is exactly what I achieve by upgrading to C1

No, I was talking about something else, upon request you can remove the altitude limitation completely and fly up several kilometers

Hi there,
thank you for reaching out.

To confirm, the "H" always represents altitude relative to the take-off point, not the home point.

Should you have any other questions, feel free to contact us. Thank you.

DJI Diana Posted at 9-8 02:28
Hi there,
thank you for reaching out.

Thank you Diana, nice to know.

fgange57 Posted at 9-7 00:28
I suspected that, I just hope this will change later.  In the meantime, I will just have to raise the max height when doing hiking in the mountains :-).

How would the drone know the height above the ground at the new position?

The 120m rule is measured from take off height which the drone knows. The fact that this is also usually the ground level at time of take off is coincidental. (If you take off from the top of a tall building the ground level may be well below you, but the rule applies to height from take off height).

When you update you home point the drone doesn't know what height it is above the actual ground level as it has no database of ground levels against GPS position. The best it could do is to guesstimate based on the downward sensors which only work up to a certain height above the ground (I forget what height that is) and so would be useless in most (?) situations.

No Original Thought Posted at 9-8 03:43
How would the drone know the height above the ground at the new position?

The 120m rule is measured from take off height which the drone knows. The fact that this is also usually the ground level at time of take off is coincidental. (If you take off from the top of a tall building the ground level may be well below you, but the rule applies to height from take off height).

It should not be that difficult as long as rules are being set. I know that I get a warning when my drone is at at least 2,4m or closer above the ground - perhaps even higher (I guess measured by the downward sensors), so of course I can calculate how much higher I can go (that is what I have to do currently).

My question was rather if DJI could use the parameters from the downward sensors (i.e. require the drone to descend that much) to decide the new height above ground when updating new home point (and e.g. issue a warning that you have to get lower to get a correct reading of the new height basis).

It is no need to over complicate this issue, and why not try to think outside the box?
Futhermore, the 120m rule apply to the distance you are to either the ground or outside of a cliff, so the rule does not refer to the takeoff point, hence DJI is restricting the flight more than intended.  Still, I accept that this is what DJI have chosen and therefore glad I got my drone upgarded to class C1, because then I can at least do my own calculation and dont have to land to continue when hiking uphill.

fgange57 Posted at 9-8 04:18
It should not be that difficult as long as rules are being set. I know that I get a warning when my drone is at at least 2,4m or closer above the ground - perhaps even higher (I guess measured by the downward sensors), so of course I can calculate how much higher I can go (that is what I have to do currently).

My question was rather if DJI could use the parameters from the downward sensors (i.e. require the drone to descend that much) to decide the new height above ground when updating new home point (and e.g. issue a warning that you have to get lower to get a correct reading of the new height basis).

The manual gives some information concerning the range of the downward looking sensors.

"Downward Vision System Precision Measurement Range: 0.3-12 m;
FOV: 106° (front and back), 90° (left and right)
Hovering Range: 0.5-30 m"   <- badly phrased I think, or what on earth does that mean.

"Effective Sensing Speed: Flight Speed ≤ 5 m/s"

I'd expect the maximum range to be somewhere around the 30m mark, you can check this by sending the drone up to say 100m and fly it over the roof of your house etc. then close the throttle and hold it closed.
The drone will presumably descend at initially 5m/s but probably slow down a bit when the drone's downward looking sensors detect the roof, just be ready incase that does not happen.

Whilst those sensors control the descent rate they are not, as far as I know, used by the drone for anything else and I doubt they control the drone's height in free flight except when an object is within 50cm of the bottom of the drone.
Plus if DJI did program them into height control I think there would be screams of anguish because the drone was pogoing up and down as it passed over every rock, bush and tree on the ground, as has already happened with the landing protection 50cm thing.

Sean-bumble-bee Posted at 9-8 06:54
The manual gives some information concerning the range of the downward looking sensors.

"Downward Vision System Precision Measurement Range: 0.3-12 m;

Hi Sean,
Thank you for useful information.

I was not thinking about a continually  check of the height above ground, only when you go into the menu "Update Home point".

Regarding warning "Close to ground", I recently experienced descending from 38 meters and got a warning of being 2,7m from ground when I was 8m above a river, so I don't think the warning itself will come very much earlier than 2,5-3m.  The issue I experienced was a high power line below me that I could not see visually (even if I could see the drone), but had I looked at the screen (which I did when I got a warning that the drone was landing).  The drone actually perceived the high power line as ground and since I was descending I sort of forced landing.  The main problem was that it was a lot of river roar where I were standing, so I did not hear the warning.  Anyway I definitely got a warning in free flght.
This can be seen from 2:15 on this video: PS. At the last part of the video, you can see that the drone lands (due to low battery) without me being able to stop it. Landing protection?

Only with 3rd party app you can use ground elevation and that is for recording and mapping. Then drone follow therian. Only few of them as enterprise 3t can do ground elevation with down sensor but only on max height with 180-200m. Everything else i agree with No Original Thought post.

fgange57 Posted at 9-9 00:55
Hi Sean,
Thank you for useful information.

Yes you should be able to cancel RTH with button on RC by one press. Because you were in low battery warning (yellow line). And you can gain full control of your drone. When you enter in critical battery warning drone will automatically land. Also u had in that situation two big enemy for drones. Water and power lines. Water refflection have effect on down sensors, and power lines like antenas can disrupt compas and all sensors. As i can see you where very lucky with that flight.

Benzinac Posted at 9-9 08:17
Only with 3rd party app you can use ground elevation and that is for recording and mapping. Then drone follow therian. Only few of them as enterprise 3t can do ground elevation with down sensor but only on max height with 180-200m. Everything else i agree with No Original Thought post.

I have been looking at several of my previous screen recordings, I can see that I get "near ground warning" that starts when I am closer than 5 meters above the ground.  Looking at the distances where these warnings appear, they seem to be very accurate.  My point is therefore that when you press "Update home point", is should be possible to program a message of e.g. "To update height above ground you have to descend to a position closer to ground" - to get this low ground measuring system.  DJI seem to have very good programmers, so I sincerely would not think this should be to much of a programming task.  You can of course not use any other measurement above ground, because neither GPS or barometric pressure is accurate enough.

Benzinac Posted at 9-9 08:32
Yes you should be able to cancel RTH with button on RC by one press. Because you were in low battery warning (yellow line). And you can gain full control of your drone. When you enter in critical battery warning drone will automatically land. Also u had in that situation two big enemy for drones. Water and power lines. Water refflection have effect on down sensors, and power lines like antenas can disrupt compas and all sensors. As i can see you where very lucky with that flight.

I know.  On this trip I got lucky several times, but also proved how resilient this drone is.

fgange57 Posted at 9-9 00:55
Hi Sean,
Thank you for useful information.

I haven't gone throught the video yet but I am disturbed by the way your 'compass' display is 'bouncing' around all over the place.
I don't have a mini 3 or 4  and rarly have the compass on display but my recollection is that when it is on display it is MUCH more stable, in terms of direction, than yours appears to be.
It might be an idea to start a thread asking if that instability is normal in the mini 4 pro etc.. And yes I have flown a mini 1 & 2 in strong turbulent wind such that I had some difficulty in getting the mini 1 home

fgange57 Posted at 9-10 00:07
I have been looking at several of my previous screen recordings, I can see that I get "near ground warning" that starts when I am closer than 5 meters above the ground.  Looking at the distances where these warnings appear, they seem to be very accurate.  My point is therefore that when you press "Update home point", is should be possible to program a message of e.g. "To update height above ground you have to descend to a position closer to ground" - to get this low ground measuring system.  DJI seem to have very good programmers, so I sincerely would not think this should be to much of a programming task.  You can of course not use any other measurement above ground, because neither GPS or barometric pressure is accurate enough.

Yea that would be nice to do in dji with some sdk for down sensors. But for now drone always follow starting height. I would like too to make that like 3t enterprise ground elevation with down sensors.

Benzinac Posted at 9-9 08:32
Yes you should be able to cancel RTH with button on RC by one press. Because you were in low battery warning (yellow line). And you can gain full control of your drone. When you enter in critical battery warning drone will automatically land. Also u had in that situation two big enemy for drones. Water and power lines. Water refflection have effect on down sensors, and power lines like antenas can disrupt compas and all sensors. As i can see you where very lucky with that flight.

Also u had in that situation two big enemy for drones. Water and power lines. Water refflection have effect on down sensors, and power lines like antenas can disrupt compas and all sensors.

Flying over water doesn't create problems for the drone's sensors as you imagine.
Neither do antennas or power lines.

fgange57 Posted at 9-10 00:07
I have been looking at several of my previous screen recordings, I can see that I get "near ground warning" that starts when I am closer than 5 meters above the ground.  Looking at the distances where these warnings appear, they seem to be very accurate.  My point is therefore that when you press "Update home point", is should be possible to program a message of e.g. "To update height above ground you have to descend to a position closer to ground" - to get this low ground measuring system.  DJI seem to have very good programmers, so I sincerely would not think this should be to much of a programming task.  You can of course not use any other measurement above ground, because neither GPS or barometric pressure is accurate enough.

when you press "Update home point", is should be possible to program a message of e.g. "To update height above ground you have to descend to a position closer to ground" - to get this low ground measuring system.
But the homepoint has no height, just lat/long coordinates.
The zero height that you get at startup is completely unrelated to the homepoint.
You can of course not use any other measurement above ground, because neither GPS or barometric pressure is accurate enough.
Your drone does not use GPS for height measurement and the barometric sensor is quite accurate enough for most flyers, most of the time.
It would be very rare that anyone would need what you think you need.

Sean-bumble-bee Posted at 9-10 02:06
I haven't gone throught the video yet but I am disturbed by the way your 'compass' display is 'bouncing' around all over the place.
I don't have a mini 3 or 4  and rarly have the compass on display but my recollection is that when it is on display it is MUCH more stable, in terms of direction, than yours appears to be.
It might be an idea to start a thread asking if that instability is normal in the mini 4 pro etc.. And yes I have flown a mini 1 & 2 in strong turbulent wind such that I had some difficulty in getting the mini 1 home

The behaviour of the compass is apparently normal (RC 2 compass too sensitive, I have been told).  It was even worse earlier.  The easy way of of this is simply to swap places on the radar between the drone and the controller (the drone in the middle).  Then it is steady.

Labroides Posted at 9-10 05:12
when you press "Update home point", is should be possible to program a message of e.g. "To update height above ground you have to descend to a position closer to ground" - to get this low ground measuring system.
But the homepoint has no height, just lat/long coordinates.
The zero height that you get at startup is completely unrelated to the homepoint.

I can't see anything new in your reply (and nothing I didn't know).  If you go hiking and go uphill (we have quite a lot of mountain areas in Norway) and start filming going upwards, you really don't get very far before the 120m limit hits you.  If you don't think that anyone would need what i suggest, I guess you live in a flat area?

Labroides Posted at 9-10 05:08
Also u had in that situation two big enemy for drones. Water and power lines. Water refflection have effect on down sensors, and power lines like antenas can disrupt compas and all sensors.

Flying over water doesn't create problems for the drone's sensors as you imagine.

I tend to agree with Labdroides on this, because I have been flying quite a few times over water (also quite low) and this has never caused a problem to me, and as for the power lines, I did not encounter any sensor issues - they actually warned that I was too close, but I did not hear due to the background noise). If you do as I did though - land on them - it may do some harm (to me the only thing happening was a motor shorty being blocked and the camera pushed out of position).

fgange57 Posted at 9-10 09:03
I can't see anything new in your reply (and nothing I didn't know).  If you go hiking and go uphill (we have quite a lot of mountain areas in Norway) and start filming going upwards, you really don't get very far before the 120m limit hits you.  If you don't think that anyone would need what i suggest, I guess you live in a flat area?

I can't see anything new in your reply (and nothing I didn't know).
I repeated the simple facts because you continue to ask for something more than what would work.

I guess you live in a flat area?
I live in a part of the world that doesn't force drones to stay within 120 metres of the launch point.
Did Norway go with the stupid European rule that does that?
In the rest of the world you can adjust your drone to fly up to 500 metres higher than your launch point and it's up to you to manage height above ground.

Labroides Posted at 9-10 13:25
I can't see anything new in your reply (and nothing I didn't know).
I repeated the simple facts because you continue to ask for something more than what would work.

OK, then I understand why you don't see the point in this, and yes, for some reason Norway is trying to be the best in class following European rules, even if Norway is no part of EU.  A lot of people in power here are control freaks, but some of the reasons for the strict rules are in particular Russians flying places they shouldn't and stupid people flying into or too close to airports.  Every time a jerk breaks a reasonable rule, the rules are being even more strict.  Also, as you point out these rules goes for all of Europe, so I guess you live in the States, where I guess Russian tourists are less of a problem :-).

Labroides Posted at 9-10 05:08
Also u had in that situation two big enemy for drones. Water and power lines. Water refflection have effect on down sensors, and power lines like antenas can disrupt compas and all sensors.

Flying over water doesn't create problems for the drone's sensors as you imagine.

You are wrong on this. I have a years experience with Mavic 2. I'm using them for mapping cell tower in most part of Europe. Sometimes after one tower and sometimes after 10 tower i get error for sensors and always need recalibration. And for water reflection, down sensors can give your wrong ati and you can easily crush your drone. So you have drones with one puck RTK and two puck RTK. Still one is not enough for high-voltage inspection you need two. Same is with compass. But on compass metal makes interference.

Benzinac Posted at 9-11 11:21
You are wrong on this. I have a years experience with Mavic 2. I'm using them for mapping cell tower in most part of Europe. Sometimes after one tower and sometimes after 10 tower i get error for sensors and always need recalibration. And for water reflection, down sensors can give your wrong ati and you can easily crush your drone. So you have drones with one puck RTK and two puck RTK. Still one is not enough for high-voltage inspection you need two. Same is with compass. But on compass metal makes interference.

Perhaps you are talking about getting in to just a couple of metres from cell towers or power lines?
Most drone flyers aren't doing that and will never experience any effect from cell towers or power lines.

And for water reflection, down sensors can give your wrong ati and you can easily crash your drone.
As for this "advice" ... it's complete nonsense and I'll ignore it.

fgange57 Posted at 9-10 00:07
I have been looking at several of my previous screen recordings, I can see that I get "near ground warning" that starts when I am closer than 5 meters above the ground.  Looking at the distances where these warnings appear, they seem to be very accurate.  My point is therefore that when you press "Update home point", is should be possible to program a message of e.g. "To update height above ground you have to descend to a position closer to ground" - to get this low ground measuring system.  DJI seem to have very good programmers, so I sincerely would not think this should be to much of a programming task.  You can of course not use any other measurement above ground, because neither GPS or barometric pressure is accurate enough.

My point is therefore that when you press "Update home point", is should be possible to program a message of e.g. "To update height above ground you have to descend to a position closer to ground" - to get this low ground measuring system.  DJI seem to have very good programmers, so I sincerely would not think this should be to much of a programming task.
Although this is very easy to do technically, DJI will never do this, because it would mean breaking the law in Europe and probably in other countries.
European law obliges the drone to stay at a maximum of 120 m (500 m for others) from the take-off point, not from the home point. In a single flight, a drone can have only one take-off point and a lot of home points

because neither GPS or barometric pressure is accurate enough.
They have a sufficient precision of 0.5m.
  
Why don't the height above ground update when Home Point is updated?
Because they are two different things. The take-off point is not a home point and can only be changed... by another take-off

Labroides Posted at 9-11 14:54
Perhaps you are talking about getting in to just a couple of metres from cell towers or power lines?
Most drone flyers aren't doing that and will never experience any effect from cell towers or power lines.

Small orbit 10m large orbit 30m from cell tower. As for watter when we had recording commercial at the The Blue Lagoon in Malta. It was sunny day and evry time when we have take off with inspire from boat we got negative atti when we where flying acros watter. And that is with ispire 2. In late hours (golden hour) we did not have that problem. So first you need to expirience something and then shere to people. Dont stick to the book and papper.

Va1entin2 Posted at 9-11 22:28
My point is therefore that when you press "Update home point", is should be possible to program a message of e.g. "To update height above ground you have to descend to a position closer to ground" - to get this low ground measuring system.  DJI seem to have very good programmers, so I sincerely would not think this should be to much of a programming task.  
Although this is very easy to do technically, DJI will never do this, because it would mean breaking the law in Europe and probably in other countries.
European law obliges the drone to stay at a maximum of 120 m (500 m for others) from the take-off point, not from the home point. In a single flight, a drone can have only one take-off point and a lot of home points

I have to correct you here regarding the 120m limit. I am very familiar with the Norwegian (and European) legislation concerning this issue.  The legislation says that you can fly 120m above ground (or near to a cliff side or similar).  It does not mention the start point. Ref: "The drone must always fly within 120 meters of the closest point of the earth".
and: "The new regulations change the old rule of flying the drone maximum of 120 meters vertically from the ground. Instead, it is a maximum of 120 meters from the nearest point of the earth, which is the limit. It is also possible to fly even higher if you fly within 15 meters of an artificial object and have the owner's approval."
To give an even better explanation, please se the picture below.

Benzinac Posted at 9-12 00:26
Small orbit 10m large orbit 30m from cell tower. As for watter when we had recording commercial at the The Blue Lagoon in Malta. It was sunny day and evry time when we have take off with inspire from boat we got negative atti when we where flying acros watter. And that is with ispire 2. In late hours (golden hour) we did not have that problem. So first you need to expirience something and then shere to people. Dont stick to the book and papper.

It's completely normal for the barometric sensor to be +/- 10  metres or so during a flight, so I can't make sense of your warning.
Even if it was showing negative altitude, that doesn't mean you have a problem or that the drone is going to crash.

So first you need to expirience something and then shere to people. Dont stick to the book and papper.
I've only flown thousands of kilometres over the sea in the last 10 years, so what would I know?

Labroides Posted at 9-12 02:54
It's completely normal for the barometric sensor to be +/- 10  metres or so during a flight, so I can't make sense of your warning.
Even if it was showing negative altitude, that doesn't mean you have a problem or that the drone is going to crash.

You did not understand. I had problem on low atti above sea with down sensor precission becouse of reflection. On higher atti did not have that problem also when sun is low. Drone will not fall down byself. Im talking about what can cause sensors to be inaccurate. Also my friend crashed mini 3 pro with sensors on becouse he try to fly between two bridge colums that were too close to each other. Drone just get magnetic interference and drifted on left side and hit colum.

Benzinac Posted at 9-12 04:52
You did not understand. I had problem on low atti above sea with down sensor precission becouse of reflection. On higher atti did not have that problem also when sun is low. Drone will not fall down byself. Im talking about what can cause sensors to be inaccurate. Also my friend crashed mini 3 pro with sensors on becouse he try to fly between two bridge colums that were too close to each other. Drone just get magnetic interference and drifted on left side and hit colum.

You did not understand.
You are correct .. It's difficult to understand and I can't tell if it's your writing or your story.

Also my friend crashed mini 3 pro with sensors on becouse he try to fly between two bridge colums that were too close to each other. Drone just get magnetic interference and drifted on left side and hit colum.
I wonder if it was really a magnetic interference issue or just losing GPS and not properly flying the drone in atti mode?
Did anyone analyse the data to properly find the actual cause or did someone just guess?

Labroides Posted at 9-12 04:59
You did not understand.
You are correct .. It's difficult to understand and I can't tell if it's your writing or your story.

It has obstical sensors on. But i will try to find video. And sen to you  you. And give me fedback of your opinion.

fgange57 Posted at 9-12 01:48
I have to correct you here regarding the 120m limit. I am very familiar with the Norwegian (and European) legislation concerning this issue.  The legislation says that you can fly 120m above ground (or near to a cliff side or similar).  It does not mention the start point. Ref: "The drone must always fly within 120 meters of the closest point of the earth".
and: "The new regulations change the old rule of flying the drone maximum of 120 meters vertically from the ground. Instead, it is a maximum of 120 meters from the nearest point of the earth, which is the limit. It is also possible to fly even higher if you fly within 15 meters of an artificial object and have the owner's approval."
To give an even better explanation, please se the picture below.

You can't correct me, because I didn't make a mistake, you made a mistake. What you posted are the requirements for the A1 subcategory and they refer to the pilot's obligations.
The requirements for category C0 refer to the obligations of the drone manufacturer, not the pilot. And here's what EASA says about the C0 qualification requirements::

A class C0 UAS shall comply with the following:
(1) have an MTOM of less than 250 g, including payload;
(2) have a maximum speed in level flight of 19 m/s;
(3) have a maximum attainable height above the take-off point limited to 120 m;

https://www.easa.europa.eu/en/do ... aft-systems?page=19