Hi there,
i would appreciate if anyone could give me more insight about how exactly the flight altitude calculation works at DJI drones, especially at mini 4 pro...
I am about to create a waypoint mission that needs to be wery accurate especially in terms of altitude and therefor i need to know what can i do to increase the accuracy and minimize the errors.
How is altitude determined? Is it airpressure based only, or is it a combination of airpressure and satelites data?

- Will i increase the accuracy if i pick for the flight days when airpressure is stable?
- Will i increase the accuracy if, while on ground i will wait for 32 and more satelites and update the homepoint once 32 satelites reached and start the  mission then?
- What else can i do to increase the accuracy of altitude calculation?
- Any recommended settings in order to get the best results?

Thanks

What do you mean by "need to be very accurate" ?

LV_Forestry Posted at 4-29 23:56
What do you mean by "need to be very accurate" ?

it means that 55m above HP needs to be 55 today, tomorrow and after tomorrow... allways. not 54 neither 56, but 55 each time

Afarkas Posted at 4-30 00:16
it means that 55m above HP needs to be 55 today, tomorrow and after tomorrow... allways. not 54 neither 56, but 55 each time

The precision of consumer series drones is too low to ensure this.  

It is better to use a drone equipped with a GNSS “RTK” receiver which can ensure accuracy of the order of centimeters.

LV_Forestry Posted at 4-30 00:27
The precision of consumer series drones is too low to ensure this.  

It is better to use a drone equipped with a GNSS “RTK” receiver which can ensure accuracy of the order of centimeters.

sorry, bro, my question was not "what should i buy to get cm precise altitude" ... the question was what can i do to increase the precision on m4p

Afarkas Posted at 4-30 00:33
sorry, bro, my question was not "what should i buy to get cm precise altitude" ... the question was what can i do to increase the precision on m4p

There is no way to do that, unless using appropriate device.

LV_Forestry Posted at 4-30 00:35
There is no way to do that, unless using appropriate device.

every measurement and calculation relies on conditions... im seeking to know which conditions produces more errors and which guarantees more accuracy and more consistency

The GNSS used in single mode itself has already a standard deviation of few meter. Especially in vertical which is the most complicated to solve.

If you ask for 55m +/-5m i would say yes no problem, fly with the drone having constantly clear view of the sky..

But it is totally Utopic to think that you will achieve 55m precisely at each flight no matter what you do as preparation work.

In addition the altitude tagged in EXIF is some function of GNSS + Baro, which is well known to be inaccurate. Some users here have huge experience in this field with consumer drone and can tell more. PM Labroides or wait until he react to this thread because he probably will.

How is altitude determined? Is it airpressure based only, or is it a combination of airpressure and satelites data?
From air pressure alone.
GPS is not used for height.

Will i increase the accuracy if i pick for the flight days when airpressure is stable?
Air pressure usually doesn't change enough over the duration of a flight for this to be a concern.

Will i increase the accuracy if, while on ground i will wait for 32 and more satelites and update the homepoint once 32 satelites reached and start the  mission then?
No

What else can i do to increase the accuracy of altitude calculation?
Nothing

Any recommended settings in order to get the best results?
No

Why do you need exact height each time you fly?

Labroides Posted at 4-30 02:56
How is altitude determined? Is it airpressure based only, or is it a combination of airpressure and satelites data?
From air pressure alone.
GPS is not used for height.

Thank you very much for the valuable information.
So if the altitude calculation is based on airpressure alone, the only thing in order to get the best possible accuracy and consistency is to:
- avoid performing the mission in days when drastic weather changes are coming into the area
- avoid performing the mission in the parts of the day (at sunrise and sunset) when the temperature (which means also airpressure) changes are the most dramatic
- perform the mission at the most stable weather conditions and ill get the best performance the sensors and software can provide
- gps play no role

I need the consistency and accuracy to have seasonal video the most possible same at each take, in order to be able to align the takes later at cut... and also to avoid collision, as my video end by a near fly by at church tower and i need to avoid situation like this morning:

Thanks again

Afarkas Posted at 4-30 03:51
Thank you very much for the valuable information.
So if the altitude calculation is based on airpressure alone, the only thing in order to get the best possible accuracy and consistency is to:
- avoid performing the mission in days when drastic weather changes are coming into the area

I need the consistency and accuracy to have seasonal video the most possible same at each take, in order to be able to align the takes later at cut... and also to avoid collision, as my video end by a near fly by at church tower

You'll have to launch from the same place each time for altitude to be consistent.
With the wideangle lens your drone has, an altitude difference of a few metres won't make much difference visually.
Be careful with obstacles and avoid using waypoints to fly close to them.
GPS position accuracy isn't perfect and will be +/- a few metres.

Labroides Posted at 4-30 04:05
I need the consistency and accuracy to have seasonal video the most possible same at each take, in order to be able to align the takes later at cut... and also to avoid collision, as my video end by a near fly by at church tower

You'll have to launch from the same place each time for altitude to be consistent.

launching from the same spot, thats clear. The visual identity is not affected as much by the focal lenght as by the distance of the nearest objets... the more distant they are, the less difference you see from changing positions - the more close they are the bigger difference you get with the slightest position change no matter the focal lenght

Afarkas Posted at 4-30 04:44
launching from the same spot, thats clear. The visual identity is not affected as much by the focal lenght as by the distance of the nearest objets... the more distant they are, the less difference you see from changing positions - the more close they are the bigger difference you get with the slightest position change no matter the focal lenght

the more close they are the bigger difference you get with the slightest position change no matter the focal length.
Setting waypoints close to obstacles is asking for trouble.
The horizontal position accuracy of GPS is quite variable.

Labroides Posted at 4-30 06:33
the more close they are the bigger difference you get with the slightest position change no matter the focal length.
Setting waypoints close to obstacles is asking for trouble.
The horizontal position accuracy of GPS is quite variable.

The horizontal is safe the whole mission, nothing is close. The only critical point is this one. Im standing on a great spot to see whether the height is safe and i can stop the mission if not. Here is no issue of safety, only thing is to keep the image good to look at - this morning it was just too close to be good

Hi, Afarkas. Thank you for reaching out. The aircraft's altitude calculation is based on satellite and barometer fusion. The error will be relatively large and it is not suitable for scenes that require particularly high accuracy. If you need high-precision waypoint flight, it is recommended to consider industry-level drones. Consumer aircraft series are not suitable for high-precision waypoint flight.

DJI Gamora Posted at 5-3 03:51
Hi, Afarkas. Thank you for reaching out. The aircraft's altitude calculation is based on satellite and barometer fusion. The error will be relatively large and it is not suitable for scenes that require particularly high accuracy. If you need high-precision waypoint flight, it is recommended to consider industry-level drones. Consumer aircraft series are not suitable for high-precision waypoint flight.

Hi, no i dont need industry-level high precision. Im just seeking for what conditions i can give to m4p to get the best out of it - just get the best m4p can do if have the ideal conditions.Thanks

Afarkas Posted at 5-3 07:37
Hi, no i dont need industry-level high precision. Im just seeking for what conditions i can give to m4p to get the best out of it - just get the best m4p can do if have the ideal conditions.Thanks

HI, Afarkas. The waypoints in a waypoint flight task are recorded based on the GPS positioning information. The GPS positioning accuracy will be affected due to external factors such as errors in satellite signal reception and environmental interference. Therefore, when you perform a waypoint flight task based on a previously saved flight route, there might be flight route differences between the current and previous tasks.

It is recommended that you perform a waypoint flight task based on a previously saved flight route when sufficient GPS satellites can be found. To minimize the flight route difference between two waypoint flight tasks, we recommend that you perform the two tasks within a short period of time. You can also perform post-editing to reduce the differences in the generated videos. Thank you for your understanding.