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What EXACTLY wil RTH do with NFZ?
1996 28 2016-1-25
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Wolfiesden
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A thought occured to me this weekend.

Scenario: You take off from a location at the perimiter of a NFZ.  You are to the North East of it.  You fly north around the perimiter to a point to the North West of the NFZ.  This places the northern edge of the NFZ in a direct line between you and your bird.

What happens if RTH is initiated?

Does it fly straight home, even though it would transit a NFZ?  Does it figure out that it has to fly around the NFZ to get home?  What will it do? Does it begin flying home and reach the NFZ and then force land?  Does it start to fly home, reach the NFZ perimiter and fall out of the sky?

What will it really do?

Also, with dynamic home points, say you take off outside a NFZ.  Then while you are flying and riding in a car, the car enters a NFZ.  At that point RTH is triggered, will the bird fly INTO an NFZ to land at "home" ?



I would appreciate a DJI rep come in here and explain how the logic is programmed in the situation that RTH directs the craft into a NFZ.  

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koine777
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Its explained here:

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DJI-Ken
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The above post and video explains how the NFZ works but doesn't answer your question.

First off, you will see the outline of the NFZ on your map, so if there's something around the edge of a NFZ  then you should get your photos videos where you are then land and go over to the other part where you want to fly then take off from there.

If you don't do that and fly around the outer edge, if you lose RC signal than the RTH os going to bring it back in a straight line. Since the straight line would go through a NFZ it would hit that perimeter and then land.
And if you did this and lost your aircraft, it would be all on you and a fault of DJI.
The manual says it comes home in a direct line, it's not going to come home at an arc and skirt around the NFZ perimeter.
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mike.wildlight
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DJI-Ken Posted at 2016-1-26 04:34
The above post and video explains how the NFZ works but doesn't answer your question.

First off, yo ...

Very dangerous behaviour, in my view,
Balance the risk of maybe hitting something in the air (slight) vs definitely hitting whatever is on the ground in an uncontrolled fashion.
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Wolfiesden
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DJI-Ken Posted at 2016-1-25 12:34
The above post and video explains how the NFZ works but doesn't answer your question.

First off, yo ...

So the correct answer to this is that the craft will hit the edge of the NFZ and land at that point?  Correct?

Look guys, I am not doing this nor did I do this.  I am asking so I can understand the logic that operates the craft when RTH is triggered.  I want to know what it will do in various circumstances.

I was kinda hoping it would go around but I am very happy it won't transit through a NFZ on its own.  That is precisely what I don't want it to do.  I would much rather it crash and burn than to autonomously fly across an airport runway.
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DJI-Ken
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Wolfiesden Posted at 2016-1-26 03:39
So the correct answer to this is that the craft will hit the edge of the NFZ and land at that poin ...

Yes, correct. It will stop when it hits the zone and land onto whatever is beneath it.
It would be nice if it skirted around the zone while coming home but unfortunately not the case.
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[RCG]Balthazar
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DJI-Ken Posted at 2016-1-25 20:42
Yes, correct. It will stop when it hits the zone and land onto whatever is beneath it.
It would be ...

Could it be set to Hover so the pilot has a chance to regain control before it lands?
If not maybe it's an idea to consider for the code heads
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DJI-Ken
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[RCG]Balthazar Posted at 2016-1-26 03:47
Could it be set to Hover so the pilot has a chance to regain control before it lands?
If not maybe ...

As part of your preflight, you should always set the RTH altitude to your conditions.
Right under Failsafe mode (where you adjust RTH height), is RC signal lost, from there you can set it to return to home, hover, or land.
So you do have a choice.
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Wolfiesden
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I think he meant HOVER instead of LAND when it encounters a NFZ while executing RTH.
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[RCG]Balthazar
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Wolfiesden Posted at 2016-1-25 20:56
I think he meant HOVER instead of LAND when it encounters a NFZ while executing RTH.

Yea spot on

In Hind Sight I think I mean HOVER whaterver reason it encouters a NFZ
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Flight Raptor
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DJI-Ken Posted at 2016-1-25 13:34
The above post and video explains how the NFZ works but doesn't answer your question.

First off, yo ...

DJI-Ken,

Thanks once again for your great insight and help.  

I have 1 question and perhaps request;
* The forced landing that DJI has implemented when you enter a NFZ seems a little reckless.   I say that because you have NO IDEA what is below the quadcopter when you are forcing it to land.  What if it is a park with tons of ppl or another public area?
* My understanding is that once your quadcopter enters the NFZ and the auto landing is initiated, there is NO WAY to override this.  Again, very dangerous for the reason given above.
* Wouldn't a better implementation be to create a "wall" at the NFZ area (like you do for the beginner mode and the maximum distance settings).....why not just halt the quadcoper from entering that fending area and force the user to fly around and outside it.  Forcing the quadcopter to land is creating the exact scenario all these restrictions are trying to prevent --- uncontrollable danger to people and property.
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Wolfiesden
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Flight Raptor Posted at 2016-1-25 14:25
DJI-Ken,

Thanks once again for your great insight and help.  

Fully onboard with that.

This is sort of discussion is the exact reason I started the thread.  To hash out what the copter does and how it reacts and a bit of discussion on alternatives to those current programmed instructions.

I agree that force landing the drone, especially if the user has no way to abort it, is reckless and dangerous.  What if it was a school yard full of kids?  Or a zoo with animals?

My thoughts are that it should hover for as long as possible given battery life.  Then land when battery is critical and not before.  This would give the operator chance to get in range if that was the issue, recover the craft safely and with no danger to those on the ground except in extreme circumstances where the choice is a gently landing drone or a drone falling at terminal velocity toward earth.
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DJI-Ken
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Flight Raptor Posted at 2016-1-26 04:25
DJI-Ken,

Thanks once again for your great insight and help.  

The example I gave was a RTH in a straight line and the NFZ was in the way.
If you are outside of the zone and fly towards it, you will still have control to go backwards and not go into it.
It's clearly marked on the map in the app so I don't see how anyone could accidentlly fly into it.
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Flight Raptor
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DJI-Ken Posted at 2016-1-25 16:09
The example I gave was a RTH in a straight line and the NFZ was in the way.
If you are outside of  ...

Still disagree with your implementation.   The entire reason all of the measures from the FAA and all these discusssions about geofencing are even occurring is b/c of people doing stupid things and not safely controlling their aircraft.

By DJI implementing this 'feature' of forced landing, DJI itself is creating the very unsafe situation everyone is trying to regulate.  Forcing a landing when you cannot ever possibly know exactly what is below it.  You yourself are violating VLOS of your craft by totally taking contol of the landing and not allowing the real person who is there that has VLOS to control the craft to a safe area.

Also, your comment about how anyone couldn't possibly fly into an NFZ is a weak argument.   GPS accuracy can be anywhere from 15 - 50 ft.  Most people are using the FPV capabilities of the quadcopter camera as their primary view on their tablet or phone...meaning the map in the lower corner is very small and you aren't going to be easiliy able to tell if you are right on that GEOFENCING line.  There could be good photo opportunies at the very boundary of the redzone, perfectly legal to shoot and if your quadcopter happens to drift 15-30 ft into the redzone, you will automatically land.....very unsafe.

BTW....your answer for the specific example given is ALSO an unsafe implementation for the exact reason I gave in the preceding pararagraphs.

WHY won't DJI even consider what we've just mentioned here?  Halt and hover....literally, like a fence...you simply cannot go past it, but do not force the craft to land.

  
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Wolfiesden
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FR,

I think you are jumping the gun here a little too.  Ken did not say it would force land if it encountered a NFZ.  He said it would do so if it hit an NFZ and WHILE currently in RTH mode.  Different scenario.

I don't believe it would auto land if it drifted to a NFZ.  Ken?

In the case of a RTH situation, i do agree with FR, force landing it an inappropriate action here.  I firmly believe, unless you can state a good reason not to, that it should hover for as long as it can giving the operator the best chance to recover control and safely navigate the drone.  Only once the battery becomes critical and the drone determines it can no longer remain safely airborne, only then should it initiate any sort of landing procedure.

The rule should be if it can safely stay aloft, it should stay aloft.  If it can't due to mechanical, electrical, or power concerns, then land.  Clearly a falling drone is more dangerous than a landing one.  But a statationary hovering one is even safer!
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DJI-Ken
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Flight Raptor Posted at 2016-1-26 05:22
Still disagree with your implementation.   The entire reason all of the measures from the FAA and a ...

I have some updated info.
If you fly into a NFZ zone, your aircraft will go into RTH mode and will turn around and head home.
Now if you cancel RTH while it's in the zone it may land but you still have altitude control. So you can run over and get it before it hits something.
I'm not 100% sure if you'll have pitch/roll control.
So there's no fear of the aircraft hitting anything, just let the RTH bring it outside of the NFZ and then cancel.
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[RCG]Balthazar
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If I remember correctly the GeoFence was intended to be just that: A (Virtual) Fence.
I think we're talking in a big letters here but I for one would like to have the Fence as an option.
Not gonna bicker about it though
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Flight Raptor
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DJI-Ken Posted at 2016-1-25 16:47
I have some updated info.
If you fly into a NFZ zone, your aircraft will go into RTH mode and will ...

Hi Ken,

Thanks for the clarification and update.  That is 'slightly' better, but I still do not understand DJI's position on forcing a RTH or even forcing it to land.  There is absolutely ZERO need for the craft to return or land if your geofencing stops the quadcopter from entering into those fenced areas.  You maintain the desired 'keepout' region and don't force the craft to do something that may actually cause potential confusion and 'panicky' reactions from the user.  Simply having the quadcopter hit a virtual wall and go not further should be more than sufficient.

I find the comment of 'running over to the quadcopter so you can catch it before it lands because you can control altitude' to be a bit laughable because I cannot imagine a group of engineers sitting in a room designing this feature and explaining to their management that this is how they will implement it.
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Flight Raptor Posted at 2016-1-26 15:02
Hi Ken,

Thanks for the clarification and update.  That is 'slightly' better, but I still do not u ...

Perhaps you could go back and read the initial question? The OP asked what would happen if the aircraft entered RTH mode while on the other side of an NFZ. Ken explained it quite clearly in the end.

"GPS accuracy can be anywhere from 15 - 50 ft."

Not true at all, the GPS sub-system on the Phantom is capable of much greater accuracy than that. You are talking about the accuracy you would get with a cell phone, the GPS DJI use is several orders better than that. Any serious GPS module can resolve to an accuracy of under 2 Metres and the best are down to millimetres.



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DJI-Ken
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[RCG]Balthazar Posted at 2016-1-26 06:46
If I remember correctly the GeoFence was intended to be just that: A (Virtual) Fence.
I think we're  ...

Yes, but the no-fly zone is also a fence. But if you are going full speed it may go into it 50ft or so until it stops then will go into RTH mode.
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DJI-Ken
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Flight Raptor Posted at 2016-1-26 12:02
Hi Ken,

Thanks for the clarification and update.  That is 'slightly' better, but I still do not u ...

If you are going full speed and ignore the warning that you are approaching a NFZ then it will enter the zone and then slow to a stop and go into RTH mode. The refresh rate of the GPS is not quick enough to make it go from full speed to a stop just a few feet from the zone. But you do get plenty of warning that you are approaching it. And if you ignore it and continue at full speed then it goes into RTH, I would think it's your fault because you ignored the it gave you.
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DJI-Ken
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Geebax Posted at 2016-1-26 12:22
Perhaps you could go back and read the initial question? The OP asked what would happen if the airc ...

GPS accuracy is only a few feet, but the refresh rate would not stop it in time, it would slowly slow down after it entered the zone.
I still don't get what the complaints are about. It gives you plenty of warning about you approaching the NFZ, When it does stop and turn around.
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DJI-Ken Posted at 2016-1-26 16:23
GPS accuracy is only a few feet, but the refresh rate would not stop it in time, it would slowly s ...

I think it would be great if someone could test this out in practice on a nice benign NFZ and report their findings back here. I have one very close to me, but at the moment I cannot get in the air, otherwise I would test it out.
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Geebax Posted at 2016-1-26 13:30
I think it would be great if someone could test this out in practice on a nice benign NFZ and repo ...

I may try it this week if I get time.
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Flight Raptor
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Wolfiesden Posted at 2016-1-25 16:46
FR,

I think you are jumping the gun here a little too.  Ken did not say it would force land if it e ...

Totally agree with your post !
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Flight Raptor
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I do appreciate everyone's post here as this is new territory for me.  I have never come close to a NFZ, so never tested this, so I anxiously await anyone's empirical data on this.  Comments on actual GPS accuracy are noted and I stand corrected.
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DJI-Ken
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Flight Raptor Posted at 2016-1-26 22:58
I do appreciate everyone's post here as this is new territory for me.  I have never come close to a  ...

The accuracy is +/- 1.5m when hovering, so at full speed it can't possibly keep that accuracy.
And I think 1.5m is very conservative, every Phantom/Inspire  I've had with a perfect  IMU and compass calibration would hover within less then 1/2m and wouldn't move up of down much at all even in a little bit of wind.
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Wolfiesden
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DJI-Ken Posted at 2016-1-26 09:36
The accuracy is +/- 1.5m when hovering, so at full speed it can't possibly keep that accuracy.
And  ...

Yes, that has been my experience with both my P3A and the P3P.  They have been very accurate.

Consumer GPS signals are intentionally corrupted by the governments that own them.  It used to be far worse with "Selective Service".  They purposefully introduce errors into the streams.  With selective service in full operation, it was a wider error margin.  Supposedly turned off but don't believe it.  It was simply turned down to a smaller error rate.  

And here is another little tidbit of insanity...one arm of our (US) government set about countering that error with D-GPS (differential GPS).  The USCG set up GPS receivers at known locations, they received their location via GPS, subtracted their actual location to know the error that was introduced to GPS and then rebroadcasted the error correction.  D-GPS enabled receivers then received their own GPS position as well as the signal from the USCG radio beacons and did the math to come up with GPS that was accurate to down to about the width of a 2x4.  So what the US military corrupted, the USCG uncorrupted.  Billions of dollars spent on both sides against each other.  Utter stupidity at work.

I have a sneaking hunch DJI is using the Soviet GLONAS against GPS and comparing the two and averaging them to counter the intentional errors introduced since GLONAS errors are not the same error that GPS has.  A bit of quick math gets you a damn accurate position.

Why the errors?  Well they told us so that ICBM's can't hit their specific target.  Yea, right.  Like a freakin nuke cares if its 10' off.  Or for that matter a mile off.  Its still vaporizing most of the city.  Right?
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Wolfiesden Posted at 2016-1-27 02:02
Yes, that has been my experience with both my P3A and the P3P.  They have been very accurate.

Con ...


"selective service"  was turned off some years ago (2000?) as an everyday thing but the ability to implement is still maintained.  The military has a far more accurate system because of exclusive use of dual band signals which allow for very accurate atmospheric corrections. GLONASS of course improves the accuracy simply because there is a lot more data coming in for the processor.

The positional stability of the Phantom's hover is not solely related to GPS accuracy it is a combination of that and the IMU.

Edit: for some additional info...

Selective service is gone and will stay gone!
See this link
http://www.gps.gov/systems/gps/modernization/sa/
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