Hi Friends,

I am new user, please suggest me on one thing, the RTH.

01. I fly from a apartment roof, it is already 50 meter above from the actual groud / street level
02. When I fly my mini 2, its captures my roof at RTH and hegiht from the roof height
03. I fly around 900 feet away, as distance from RTH, and the drone now above the actual ground
      Q 01. does the height related to actual groud or the roof from where started?
04. Now if I click on RTH [I saved as 100 meter for RTH]
      Q 02. Will it calcualte from the ground or from the roof height to move to 100 meter during return?

Thank you in advance.

DJI drones take the take off height as zero, as they are unable to calculate the distance to the real ground level.
So all heights are compared to the take off level.
If you set RTH to 100m and you take off at 50m height from ground level, it will RTH at 150m from ground level. RTH height is always calculated from the take off level.
Be carefull with RTH when you should fly to a higher ground (hill).

JohnDG Posted at 1-17 02:59
DJI drones take the take off height as zero, as they are unable to calculate the distance to the real ground level.
So all heights are compared to the take off level.
If you set RTH to 100m and you take off at 50m height from ground level, it will RTH at 150m from ground level.

Dear JohnDG,

Thank you and noted.

JohnDG Posted at 1-17 02:59
If you set RTH to 100m and you take off at 50m height from ground level, it will RTH at 150m from ground level.

Regarding "ground level, it will RTH at 150m from ground level."
That may confuse people, it might be better to edit the post and change that to  "ground level, it will RTH at 100m above the takeoff point irrespective of its height above the ground unless the drone is already above that 100m, in which case it will RTH at its current height."

Hello there. Good day and thank you for reaching out. For additional reference the Return to Home (RTH) function brings the aircraft back to the last recorded Home Point and lands when the GPS is signal is strong. There are three types of RTH: Smart RTH, Low Battery RTH, and Failsafe RTH. The said DJI Drone successfully recorded the home point and the GPS signal is strong, the RTH will be triggered when either the user starts Smart RTH, the aircraft battery level is low, or the signal between the remote controller and the is lost. RTH will also be triggered in other abnormal scenarios such as if there is a loss of video transmission. Thank you and fly safe always.

DJI Stephen Posted at 1-17 18:57
Hello there. Good day and thank you for reaching out. For additional reference the Return to Home (RTH) function brings the aircraft back to the last recorded Home Point and lands when the GPS is signal is strong. There are three types of RTH: Smart RTH, Low Battery RTH, and Failsafe RTH. The said DJI Drone successfully recorded the home point and the GPS signal is strong, the RTH will be triggered when either the user starts Smart RTH, the aircraft battery level is low, or the signal between the remote controller and the is lost. RTH will also be triggered in other abnormal scenarios such as if there is a loss of video transmission. Thank you and fly safe always.

[view_image]

Hi DJI Stephen

Thank you

Excellent share by Stephen. Where people run into trouble is if they are say on a small hill, and there are trees and power lines nearby, so they set RTH at 200', figuring that's plenty of height. Then, they fly around, say, a nearby rocky hill that's 350' above where they are standing. They lose sight of the drone, maybe get poor signal, because the drone is partly blocked by the 350' hill, get confused, hit RTH, and RTH runs the risk of running into the hill as it makes a beeline back to you, 200' above where your height is.  

I think actual pilots  (like, airline pilots), or just having that mindset, get tripped up by this adjusted mean height, versus actual altitude, because everything in aviation is by altitude. As a pilot you learn to just adjust that in your mind. Your airport and runway are at 2,200' elevation. You take off fly around the town and neighboring hills and countryside at 7,500' altitude, then come back around and land at 2,200'. Those are the only numbers you are dealing with. You don't even have to be an airline pilot or go to aviation school to think like this, which can be a source of confusion when flying a drone and seeing this number on RTH.  

It wouldn't surprise me if in X years, drone technology gets that sophisticated though, giving you options, interpreting for you, as an extra level of safety. Drones will also get so smart, RTH will simply avoid all obstacles, regardless of their height, and safely return to you. I can actually see this possibly in most drones by 2025 or so at the rate we're going.

Rider51 Posted at 1-18 22:16
I think actual pilots  (like, airline pilots), or just having that mindset, get tripped up by this adjusted mean height, versus actual altitude, because everything in aviation is by altitude. As a pilot you learn to just adjust that in your mind. Your airport and runway are at 2,200' elevation. You take off fly around the town and neighboring hills and countryside at 7,500' altitude, then come back around and land at 2,200'.

for the benefit of the original poster you should perhaps explain "altitude",  "adjusted mean height" and "elevation"

Today I tested my first RTH auto function, after taking the flight from my apartment roof, understood the calculation and learned for future.
A capture sharing with you...

Thank you everyone...

Rider51 Posted at 1-18 22:16
Excellent share by Stephen. Where people run into trouble is if they are say on a small hill, and there are trees and power lines nearby, so they set RTH at 200', figuring that's plenty of height. Then, they fly around, say, a nearby rocky hill that's 350' above where they are standing. They lose sight of the drone, maybe get poor signal, because the drone is partly blocked by the 350' hill, get confused, hit RTH, and RTH runs the risk of running into the hill as it makes a beeline back to you, 200' above where your height is.  

I think actual pilots  (like, airline pilots), or just having that mindset, get tripped up by this adjusted mean height, versus actual altitude, because everything in aviation is by altitude. As a pilot you learn to just adjust that in your mind. Your airport and runway are at 2,200' elevation. You take off fly around the town and neighboring hills and countryside at 7,500' altitude, then come back around and land at 2,200'. Those are the only numbers you are dealing with. You don't even have to be an airline pilot or go to aviation school to think like this, which can be a source of confusion when flying a drone and seeing this number on RTH.  

There are some nuances missed here:

In manned flight there are a number if terms and height above an airfield IS used.

Altitude above mean sea level is used as a standard measure of where an aircraft is in the vertical. It has no regard for the terrain and so AMSL could actually be underground.

Pilots set a barometric pressure offset on their altimeter to give them one of two or three readings.

Setting the 'QNH' pressure gives altitude above mean sea level for the measured local barometric pressure.

Setting the 'QFE' pressure gives the height above the airfield for which the QFE is issues

Setting 1013hPa - which is considered a 'standard pressure' gives a common global altitude and is used when flying at Flight Levels above a defined transition altitude. 1013 can also be used if you do not have access to a current QNH or QFE from an appropriate service.

Note that altitude and height are two different things in aviation.

-N.O.T.

Excellent posts, and thanks for clarity from everyone. Part of my problem is that my cousin is a commercial airline captain, and my ex was a FA, studying for a private pilot's license (she's probably a private pilot now), so before drones were even the norm, years before I owned one, aviation specs and nomenclature got into my head. That definitely does not make me a qualified teacher though. I just hope I didn't make things any more confusing than they are, while trying to simplify them.

Rider51 Posted at 1-19 10:34
Excellent posts, and thanks for clarity from everyone. Part of my problem is that my cousin is a commercial airline captain, and my ex was a FA, studying for a private pilot's license (she's probably a private pilot now), so before drones were even the norm, years before I owned one, aviation specs and nomenclature got into my head. That definitely does not make me a qualified teacher though. I just hope I didn't make things any more confusing than they are, while trying to simplify them.

I just hope I didn't make things any more confusing than they are, while trying to simplify them.
You probably did, introducing a lot of irrelevant and unnecessary things.
Drones are flown for short distances over a short time.
They rarely go far from where they were launched.
Real planes and their navigation are completely different.

Rider51 Posted at 1-18 22:16
Excellent share by Stephen. Where people run into trouble is if they are say on a small hill, and there are trees and power lines nearby, so they set RTH at 200', figuring that's plenty of height. Then, they fly around, say, a nearby rocky hill that's 350' above where they are standing. They lose sight of the drone, maybe get poor signal, because the drone is partly blocked by the 350' hill, get confused, hit RTH, and RTH runs the risk of running into the hill as it makes a beeline back to you, 200' above where your height is.  

I think actual pilots  (like, airline pilots), or just having that mindset, get tripped up by this adjusted mean height, versus actual altitude, because everything in aviation is by altitude. As a pilot you learn to just adjust that in your mind. Your airport and runway are at 2,200' elevation. You take off fly around the town and neighboring hills and countryside at 7,500' altitude, then come back around and land at 2,200'. Those are the only numbers you are dealing with. You don't even have to be an airline pilot or go to aviation school to think like this, which can be a source of confusion when flying a drone and seeing this number on RTH.  

For pilots it's even more complicated. Like the height of the drone is calculated by the barometer, it is influenced by the air presure. We, with our drones fly locally the difference in air presure is not so much.
Flying to another location, the pilots get into a total different air presure system. They have to adjust the height to the air presure at 0 level the airport where they are landing.

More expensive drones have already sensors to avoid collision, also for RTH. The mini 2 is a small less expensive drone with only a sensor on the bottom for landing.

But sure as you say, it is needed to think about the maximum RTH height in order of the surroundings. You might have avoided some obstacles. But RTH might take a straight line with some obsticles along the way.

djiuser_bd_/Shahriar Posted at 1-18 21:14
Hi DJI Stephen

Thank you

Hi there. Thank you for the reply and you are very much welcome. If you have any other inquiries or any concerns with DJI. Please feel free to post it here at DJI Forum. We are all here to help and assist you. Thank you and keep filming. .

Labroides Posted at 1-19 14:02
I just hope I didn't make things any more confusing than they are, while trying to simplify them.
You probably did, introducing a lot of irrelevant and unnecessary things.
Drones are flown for short distances over a short time.

He already said this: "That definitely does not make me a qualified teacher ". No need to pile on. He tried to help.

GaryDoug Posted at 1-20 22:05
He already said this: "That definitely does not make me a qualified teacher ". No need to pile on. He tried to help.

Pile it on?
I pointed out that what he added was irrelevant and unnecessarily confusing and I explained why so he's understand.