I discovered that when creating a waypoint during a flight with the DJI Mini 4 Pro, the stored altitude information is calculated relative to the home point, not as an absolute value above sea level. This means that the altitude data recorded for waypoints are based on the takeoff point, which is considered the home point.

This means that if launch a previously recorded waypoint mission from different takeoff point which has a different altitude, the path which the drone will follow will be offset vertically by the altitude difference of the two takeoff points.

This can result in drone running into obstables if the original takeoff point was on a higher altitude than the subquential takeoff point (i.e. when the mission was created we took of from a top of the hill, while when we re-run the mission the takeoff point was in a valley.

Luckely when I discovered this my obstacle avoidance succesfuly worked great and saved the day!

None of the online tutorials found on Youtube mentions this fact.

Btw here's a video I created by using a waypoint mision (it's a proof of a concept video ... not a production version):

All altitudes are related to the take off point,   the drone uses a barometer to calculate its height.  

Hi there, thank you for sharing your feedback with us. We're pleased to hear that you've discovered the obstacle avoidance feature and that it has worked well for you. We genuinely appreciate you for sharing this beautiful video with us and the effort you've put into it.

Keep us posted always. Thank you for your ongoing support!

"I discovered that when creating a waypoint during a flight with the DJI Mini 4 Pro, the stored altitude information is calculated relative to the home point, not as an absolute value above sea level. "

Why is any of that a surprise to you ?
Page 43 of the manual https://dl.djicdn.com/downloads/ ... _User_Manual_HR.pdf
says
"Visina Visina na točki rute s točke uzlijetanja. Obavezno uzlijećite s iste visine originalnog leta kako biste postigli veću točnost visine kada se ponovi let u načinu Waypoint Flight."
which google translates as
"Altitude Altitude at the waypoint from the take-off point. Be sure to take off from the same height of the original flight in order to achieve greater altitude accuracy when re-flying u Waypoint Flight mode."

Page 43 of the English manual offers the definition
"Altitude           The altitude at the waypoint from the takeoff point. Make sure to take off at the same takeoff altitude of the original flight to obtain higher accuracy of altitude when a Waypoint Flight is repeated."

Well of course it's in the manual, but who reads manuals when there are official DJI YouTube tutorials ...

Anyways it would be nicer if absolute drone altitude was recorded (above sea level).

I wonder which altitude is stored when creating waypoints via the map interface instead of during the flight. That's something worth testing out ...

One other interested fact is that POIs are not saved. They are only used during the initial creation of the mission and can not be re-used when editing a previously saved mission.

OT: Wonderful country. Where did you shoot?

You are correct, it's a poor limitation of waypoint. I miss my Mavic 2 where I could create waypoints online and use Litchi to fly the waypoints. There is no mony in creating good software, just new products to sell.

kneecola Posted at 7-15 04:46
Well of course it's in the manual, but who reads manuals when there are official DJI YouTube tutorials ...

Anyways it would be nicer if absolute drone altitude was recorded (above sea level).

Anyways it would be nicer if absolute drone altitude was recorded (above sea level).
But the drone has no way to measure altitude above sea level, so how would you do that?

I wonder which altitude is stored when creating waypoints via the map interface instead of during the flight. That's something worth testing out ...
Go ahead and test and learn something.
The only height the drone can measure is height relative to launch point ... launch point = zero.
So what altitude do you think would be stored???

Va1entin2 Posted at 7-15 04:56
OT: Wonderful country. Where did you shoot?

This was shot on island of Susak in Croatia

Thanks!

kneecola Posted at 7-15 04:46
Well of course it's in the manual, but who reads manuals when there are official DJI YouTube tutorials ...

Anyways it would be nicer if absolute drone altitude was recorded (above sea level).

, "but who reads manuals when there are official DJI YouTube tutorials ..."

Those with some common sense !

"Anyways it would be nicer if absolute drone altitude was recorded (above sea level)."
and of what use would that be ?

Who carries AMSL heights in their mind, drone pilots are relative ground huggers, how would Joe Bloggs plan a flight based on AMSL most of the time he wont know his own AMSL.

How would you actually implement it in a drone?

Consumer level GPS is not accurate in terms of height so you can not use GPS to calculate AMSL.
Just look at the AMSL heights in the exif data of photos takens by drones, the last time I looked I think it was 70m+ out and I was at sea level, literally.
You are left with a GPS location that represents a column of air above a point on the earth's surface.
The drone would have to carry a database of surface elevation vs location and that database would cost money. To calculate an airborne AMSL the drone would then have to compare the ground elevation below the drone against the ground elevation at the take off point and then add the drone's height above the take off point as measured by barometer.

DJI drones might estimate AMSL from air pressure, they do apparently warn you if they think you are near their maximum altiudes e.g. way up there in the Andes or Himalaya etc. but it's nowhere near accurate enough to rely on for ground clearances.

Labroides Posted at 7-15 05:43
Anyways it would be nicer if absolute drone altitude was recorded (above sea level).
But the drone has no way to measure altitude above sea level, so how would you do that?

I sense aggression in your tone. Is everything OK?

kneecola Posted at 7-15 07:24
I sense aggression in your tone. Is everything OK?

I sense that you don't like having to deal with facts and prefer to wallow in ignorance.

Sean-bumble-bee Posted at 7-15 07:06
, "but who reads manuals when there are official DJI YouTube tutorials ..."

Those with some common sense !

The DJI Mini 4 Pro determines its altitude using a combination of a barometric pressure sensor and GPS data. The barometric pressure sensor provides relative altitude information, which helps in maintaining stable flight and precise low-altitude operations. For absolute altitude (elevation above sea level), the drone uses GPS data. When the home point is set, the barometer is calibrated to the local altitude using GPS, which helps in achieving a more accurate altitude measurement during the flight.

This dual approach allows the Mini 4 Pro to ensure more reliable altitude readings, combining the rapid response of barometric pressure measurements with the absolute reference provided by GPS.

Sources:
* (https://www.dji.com/mini-4-pro/specs)
* (https://www.dji.com/support/product/mini-4-pro)
* (https://forum.dji.com/thread-208432-1-1.html)

In the end all this irrelevant. The only thing which is important is to keep in mind that the drone has this limitation when using the waypoint missi

kneecola Posted at 7-15 09:25
The DJI Mini 4 Pro determines its altitude using a combination of a barometric pressure sensor and GPS data. The barometric pressure sensor provides relative altitude information, which helps in maintaining stable flight and precise low-altitude operations. For absolute altitude (elevation above sea level), the drone uses GPS data. When the home point is set, the barometer is calibrated to the local altitude using GPS, which helps in achieving a more accurate altitude measurement during the flight.

This dual approach allows the Mini 4 Pro to ensure more reliable altitude readings, combining the rapid response of barometric pressure measurements with the absolute reference provided by GPS.

You cite three sources for your conclusion that the drone uses GPS to measure/control height, could copy and paste the relevant snippets here please. I didn't see anything in the first two sources but I did find

"In addition, the altitude is calculated by an on board barometer that detects pressure and measures the difference from when it was launched to where it is now."

in post 3 of the third one. Most of the other posts that I read in that thread seem to agree that although GPS height measurement is possible and a value is recorded in the logs but it is NOT accurate and is NOTused by the drone in determining the height shown in the app or in governing the drone's motion.

DJI Natalia Posted at 7-15 03:23
Hi there, thank you for sharing your feedback with us. We're pleased to hear that you've discovered the obstacle avoidance feature and that it has worked well for you. We genuinely appreciate you for sharing this beautiful video with us and the effort you've put into it.

Keep us posted always. Thank you for your ongoing support!

Thanks

kneecola Posted at 7-15 13:08
Thanks

Most welcome. Should you need any assistance, please do not hesitate to reach us. Thank you and have a good day !

kneecola Posted at 7-15 09:25
The DJI Mini 4 Pro determines its altitude using a combination of a barometric pressure sensor and GPS data. The barometric pressure sensor provides relative altitude information, which helps in maintaining stable flight and precise low-altitude operations. For absolute altitude (elevation above sea level), the drone uses GPS data. When the home point is set, the barometer is calibrated to the local altitude using GPS, which helps in achieving a more accurate altitude measurement during the flight.

This dual approach allows the Mini 4 Pro to ensure more reliable altitude readings, combining the rapid response of barometric pressure measurements with the absolute reference provided by GPS.

I see you are completely ignorant of how your drone measures altitude.
You are completely wrong about this.
GPS is not used for altitude measurement.

Still nice footage! I have always thought about making these transitions, but so far the waypoints are not precise enough (from what I gather at least).

Montfrooij Posted at 7-16 00:24
Still nice footage! I have always thought about making these transitions, but so far the waypoints are not precise enough (from what I gather at least).

You are correct - waypoints can be finicky. On some occasions the recorded videos matched almost perfectly and on others the change in drone position was quite noticeable.

Putting aside the technical aspects of how the drone operates "under the hood" there a few thing which might influence the outcome. Takeoff spot is one of them, but there's also wind, which can be a big factor.

I'm planing to do some more experimenting with this to figure out how to minimize the difference between flights:
* using exactly same takeoff spot
* creating waypoints on a map instead of during flight
* trying out app such as Litchi

kneecola Posted at 7-16 00:47
You are correct - waypoints can be finicky. On some occasions the recorded videos matched almost perfectly and on others the change in drone position was quite noticeable.

Putting aside the technical aspects of how the drone operates "under the hood" there a few thing which might influence the outcome. Takeoff spot is one of them, but there's also wind, which can be a big factor.

Because of the large field of view, even the slightest change in orientation can cause a big difference.
I once made a 'daylapse' where I took the same picture for many days on the exact same spot with my DSLR and a monopod.
Even that was quite difficult because the slightest variation in orientation made it difficult to align the images in post.

Montfrooij Posted at 7-16 00:55
Because of the large field of view, even the slightest change in orientation can cause a big difference.
I once made a 'daylapse' where I took the same picture for many days on the exact same spot with my DSLR and a monopod.
Even that was quite difficult because the slightest variation in orientation made it difficult to align the images in post.

So the bottom line is that this is really hard to do.

I was hoping the video editing software might help a bit via it's morphing transitions and tracking capabilities. All this makes this task all more complicated.

Well I guess we will need to set realistic goals and adjust expectations accordingly.

BTW have a look at the following video ... the camera was suspended on a cable:

kneecola Posted at 7-16 03:34
So the bottom line is that this is really hard to do.

I was hoping the video editing software might help a bit via it's morphing transitions and tracking capabilities. All this makes this task all more complicated.

Wow. That is super impressive.
Well, I'm sure software can help and with video footage it's just one transition every time.
Where I had to do 1 transition for every frame (stills).

kneecola Posted at 7-16 00:47
You are correct - waypoints can be finicky. On some occasions the recorded videos matched almost perfectly and on others the change in drone position was quite noticeable.

Putting aside the technical aspects of how the drone operates "under the hood" there a few thing which might influence the outcome. Takeoff spot is one of them, but there's also wind, which can be a big factor.

Do you realise that GPS does not have pinpoint accuracy?
Your waypoints are going to be +/- a few metres from one flight to the next.

And GPS is not used at all for altitude measurement.

I also wish that waypoint headings were recorded as True N compass headings. The way it is now, headings east of north (or south) are recorded with negative numbers. Never in the history of navigation has a control tower given an instruction to steer to a heading of -90 degrees! That would be 270 degrees.

DAFlys Posted at 7-15 00:46
All altitudes are related to the take off point,   the drone uses a barometer to calculate its height.

actually is it based on barometer or also on GPS ?- often the barometer is calibrated by GPS.
btw i noticed that when one is defining the waypoints on the map only one can not define negative waypoints. so if you start on the top of a hill and want to fly down - bad luck.

erhard52 Posted at 8-6 18:45
actually is it based on barometer or also on GPS - often the barometer is calibrated by GPS.
btw i noticed that when one is defining the waypoints on the map only one can not define negative waypoints. so if you start on the top of a hill and want to fly down - bad luck.

actually is it based on barometer or also on GPS - often the barometer is calibrated by GPS.
Except that's 100% wrong.
GPS is only used for location and horizontal position holding.

In DJI drones GPS isn't used at all for altitude or calibrating the barometer.

If you can find any proof of your statement, I'll be happy to apologise.
But until then, Iit's clear that you have no idea what you are taking about.

erhard52 Posted at 8-6 18:45
actually is it based on barometer or also on GPS - often the barometer is calibrated by GPS.
btw i noticed that when one is defining the waypoints on the map only one can not define negative waypoints. so if you start on the top of a hill and want to fly down - bad luck.

The barometer will be used to record the change in altitude but the take off point is where 0ft will be,    Put the drone on top of a wall and take off vs the ground and you'll see the difference.  

Labroides Posted at 8-6 20:32
actually is it based on barometer or also on GPS - often the barometer is calibrated by GPS.
Except that's 100% wrong.
GPS is only used for location and horizontal position holding.

ok i missed a question mark after he first part. the second part is only my experience with some handheld garmins.
so i do not dispute your comment. i just would like to know which sensors are used during which operations?

erhard52 Posted at 8-9 21:20
ok i missed a question mark after he first part. the second part is only my experience with some handheld garmins.
so i do not dispute your comment. i just would like to know which sensors are used during which operations?

i just would like to know which sensors are used during which operations?
In DJI drones it's pretty simple.
All height measurement is done with the barometric sensor (apart from the limited range of VPS sensors).
GPS is only used for location and horizontal position holding.

GPS isn't used at all for altitude and the barometer cannot be calibrated.

Labroides Posted at 8-9 21:36
i just would like to know which sensors are used during which operations?
In DJI drones it's pretty simple.
All height measurement is done with the barometric sensor (apart from the limited range of VPS sensors).

but GPS is not stable for position holding - jumps easily 1 few meters from sample to sample. i would assume to stabilize horizontal position in short term accelerometers are being used.

erhard52 Posted at 8-9 22:14
but GPS is not stable for position holding - jumps easily 1 few meters from sample to sample. i would assume to stabilize horizontal position in short term accelerometers are being used.

The point was that GPS isn't used for anything else.

There is also another thing to consider.  All the waypoints relies on GPS, so the positions will not necessary be the same even if you start from the same position (if you do the same route again).  You should also be careful to plan the route close to obstacles (because this may stop the route - which is default behaviour if an obstacle is met during a waypoint flight).

erhard52 Posted at 8-9 22:14
but GPS is not stable for position holding - jumps easily 1 few meters from sample to sample. i would assume to stabilize horizontal position in short term accelerometers are being used.

I think that you will find that, low down, the VPS system - when available, is the primary souce of position holding.
As demonstration, OUTSIDE where you have good GPS, fly a low hover over suitable ground in good light then repeat that hover in darkness with any illumination of the ground switched off. I think you will find that the hover in the latter has greater horizontal wanderings than the former.

A daft experiment I did was to put a switched on drone briefly into a plastic bag which was  alternately pressurised and then had the air sucked out of it.
The screen showed negative height and positive height respectively. NOTE briefly, I didn't want to risk over heating.

kneecola Posted at 7-16 00:47
You are correct - waypoints can be finicky. On some occasions the recorded videos matched almost perfectly and on others the change in drone position was quite noticeable.

Putting aside the technical aspects of how the drone operates "under the hood" there a few thing which might influence the outcome. Takeoff spot is one of them, but there's also wind, which can be a big factor.

This has been mentioned several times on this forum (concerning editing waypoints) - but, have you tested out the great www.waypointmap.com ?
If not, there you can export advanced/simple waypoint missions directly from a map with easy editing of all flight/camera parameters - great!

I have the Mini 4 Pro, but, I’m not sure what other Dji model it supports…

In Exif, photographs have two heights: relative to the house point (RelativeAltitude) and relative to sea level (GPSAltitude+GPSAltitudeRef).