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Flying over water
857 31 5-14 08:50
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Hrodnand
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Is  there a recommended minimum altitude to keep when flying over water?  As far as I know, the VPS (Visual Positioning System) turns off when  flying over water, which means that the drone relies only on GPS to  determine its position. That makes it risky to operate. Thanks in advance!

5-14 08:50
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RobZilla
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Not sure on minimum,  maybe 1 meter or less but I personally would not fly that low over water.

Just don't be like this guy in my area who flew his A2 in the water =>
5-14 09:10
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JEZ2
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The Vision sensors are not off over water, but they tend to not work properly.  

Right in your manual DJI recommends flying at least 3 meters over water.  That's a good recommendation if you have a visual on the drone.  Since the altitude is not always perfectly accurate, if for some reason you can't see your drone, I would say you would want more than the 3 meters and would say at least 5 is best so as to not rely on the altitude indicator.
5-14 09:12
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JJB*
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Hi,

I fly alot over water, low to very low flying.
FlyApp does not show VPS height, VPS does work over water.

The only thing to be aware of is the automated forcelanding !!

This will happen if VPS is measuring 0.5 meter actual or false reading! AND you apply full ** stick down tyo lower the drone. In that situation it will go into a forcelanding and it will land....in water ofcourse!
** 80 - 90% stick down also initiate Forcelanding after while.....

Try this out over land ; fly low at 0.5 meter with some forward speed over flat surface and apply stick down....the moment you hear landing (and see craft go lower) select UP and this will cancel the forcelanding.

Another check to see that VPS is working (controllinh height + forcelanding) ; hover in front of you at 30 meters height, select SPORT mode, apply 100% stick down and keep stick down all the time.See, when VSP sensor gets into range, the descent speed down gets less and drone will stop at 0.5 meter (still 100% down stick), after short moment it will autoland in a controlled way.

I never have any problems flying low over water, but be carefull to fly low over streaming water ; this will confuse the VPS and height control.
And fly not fast and do not stop rapidly or yaw and stop rapidly etc.  Just be gentle on the sticks !

See last part of this video > https://forum.dji.com/forum.php?mod=viewthread&tid=242483
cheers
JJB






5-14 09:48
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kyalami
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That is just amassing how long the drone was still recording under water. But I would not use it for under water videography. He he he...
5-14 10:04
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BrianKushner
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You mean like this? The trick was to make sure your VISION SENSOR was off which you cannot do in the DJI Fly app.

5-14 10:19
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JJB*
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Hi,

Not as nice as the #10, but my MM2 with VPS height sensor ON (well, you cannot disable this sensor...)  ; never probs flying low over water!



cheers
JJB
5-14 10:56
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videoeditman
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JJB* Posted at 5-14 09:48
Hi,

I fly alot over water, low to very low flying.

JJB, thanks for your informative post!
5-14 11:44
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GaryDoug
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I fly over water most of the time. I have noticed a bit more irregularity when flying over very clear water. Since the sensors are optical, I am assuming that sometimes you get the height to the bottom instead of to the surface. At least that is how it seems to me. Cloudy or silty water...no problem. Notice how the indicated height in the flight below suddenly changes by 10 feet...the water depth was about 10 feet.

185351sijti0j7tqfj8q68.png
5-14 14:42
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DJI Stephen
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Hello there Hrodnand. Good day and thank you for these information you have given. Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread on How to Fly Safely Over Water. Thank you and fly safe always.

https://forum.dji.com/forum.php?mod=viewthread&tid=181878
5-14 20:10
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Labroides
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You've got some good advice here already.

As far as I know, the VPS (Visual Positioning System) turns off when  flying over water, which means that the drone relies only on GPS to  determine its position. That makes it risky to operate.
VPS is always on on your drone.
Except when you are flying low and within the limited range of VPS, your drone is using GPS alone for positioning - that doesn't make it risky at all.
5-14 20:11
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JJB*
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GaryDoug Posted at 5-14 14:42
I fly over water most of the time. I have noticed a bit more irregularity when flying over very clear water. Since the sensors are optical, I am assuming that sometimes you get the height to the bottom instead of to the surface. At least that is how it seems to me. Cloudy or silty water...no problem. Notice how the indicated height in the flight below suddenly changes by 10 feet...the water depth was about 10 feet.

Hi Gary,

Mayby it is not what you think...., would love to see your flightlog.txt for this flight.

VPS height in Airdata.csv does always show the last height value each new record when height is out of range.
The moment the sensor is measuring again it will show correct value but the value before is the old value from many records before.

My FRAP program filters this out by use of a algorithm.
See my chart, the gray horizontal VPS height line is where old values are used, approx ID 6800 see the VPS actual height in green, the drop value gray>green is mayby what you see in your data. (blue line = baro height)


cheers
JJB




VPSheight.png
5-15 00:25
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JJB*
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DJI Stephen Posted at 5-14 20:10
Hello there Hrodnand. Good day and thank you for these information you have given. Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread on How to Fly Safely Over Water. Thank you and fly safe always.

https://forum.dji.com/forum.php?mod=viewthread&tid=181878

Stephen,

Are you sure about this?  imo vision postion is not turned off automatically
This means that flying over low over water, loosing GPS signals a DJI drone will go into ATTI and not into OPTI? Are you really sure ??
And barometer is for sure not used for positioning, but only for height control together with the bottom sensor wich cannot be disabled.

Can you explain your sentence "if affected by the accuracy range" in relation to the use of the vision sensors and the previous part of the sentence?  affected range of barometer??

cheers
JJB


5-15 00:37
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Labroides
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DJI Stephen Posted at 5-14 20:10
Hello there Hrodnand. Good day and thank you for these information you have given. Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread on How to Fly Safely Over Water. Thank you and fly safe always.

https://forum.dji.com/forum.php?mod=viewthread&tid=181878

There's no correct information in this post and all it does is to confuse anyone that reads it.
5-15 03:50
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GaryDoug
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JJB* Posted at 5-15 00:25
Hi Gary,

Mayby it is not what you think...., would love to see your flightlog.txt for this flight.

Here are the files. See what you can find about that sudden change.
Dat file is here >>> https://www.mediafire.com/file/5 ... -41_FLY097.DAT/file
However I do not think the VPS was indicating  out of range at only 19 feet. It later recorded a reading of 34 feet (real altitude of 80+ feet), more like the actual maximum. Did you think that was 19 meters?

DJIFlightRecord_2020-07-15_[12-34-01].zip

979.39 KB, Down times: 3

5-15 14:16
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JJB*
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GaryDoug Posted at 5-15 14:16
Here are the files. See what you can find about that sudden change.
Dat file is here >>> https://www.mediafire.com/file/5 ... -41_FLY097.DAT/file
However I do not think the VPS was indicating  out of range at only 19 feet. It later recorded a reading of 34 feet (real altitude of 80+ feet), more like the actual maximum. Did you think that was 19 meters?

Hi Gary,

Had a look at your log, convert the log 2x, TxtToCSV and AirData.

TxtToCSV is better, as in the csv file a column VPS active Y or N, Airdata shows the last VPS height in each next record until VPS height is active again.

See myu double chart, top is TxtToCVS, lower is AIRDATA. (oops, top - default set to meters, lower = set to feet ; but chart lines are ofcourse the same)

Your 8m7s mark is at the X-axis at 4875, height drop 19 to 9.2 feet = vertical line

In the lower chart you see a flat line, before the VPS is active measuring again, previous heigt a steady flat line of the last value of 19 feet. VPS line not visible in the upper chart as VPS sensor does not measuring height (i guess water reflections, not enough signal back to the drone).

Climbing your drone VPS height measured up to 33.8 feet, TXTtoCSV data.

PS the reason that this flat line in green is seen in the lower chart is due to my algorithm, the next flat line (further in time) is skipped (see difference up and lower chart) as the baro height > my own algorithm thresshold.

Hope it does make sense yo you, questions  just ask.

cheers
JJB
GaryVPS.png
5-16 02:44
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GaryDoug
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JJB* Posted at 5-16 02:44
Hi Gary,

Had a look at your log, convert the log 2x, TxtToCSV and AirData.

OK I get it now. Let me ask how you arrived at the VPS active status. Is that in the output of "CsvView" in the column labeled "OSD.isSwaveWork"? And is the height in the column labeled "OSD.sWaveHeight"? If not, what is your source for that?

So... a hypothetical "actual" graph might be something as shown in red below, right?

VPS possible readings.png
5-16 09:17
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JJB*
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GaryDoug Posted at 5-16 09:17
OK I get it now. Let me ask how you arrived at the VPS active status. Is that in the output of "CsvView" in the column labeled "OSD.isSwaveWork"? And is the height in the column labeled "OSD.sWaveHeight"? If not, what is your source for that?

So... a hypothetical "actual" graph might be something as shown in red below, right?

Hi Gary,

Yes, those 2 columns for the VPS height value and active value.
Your red coloured line is one of many hypthetical possibilities....

If only Airdata had all the columns like in the TXTtoCSV.....
cheers
JJB

5-16 10:48
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Montfrooij
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I have flown super low over water with my Mavic Pro.
No issues at all.
But it is a risk of course.
5-21 06:42
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Hrodnand
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51 Drones shares his unfortunate experience about crashing the Air 2S while flying over water today



7-28 09:00
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FriedChicken_II
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Hrodnand Posted at 7-28 09:00
51 Drones shares his unfortunate experience about crashing his Air 2S while flying over water today

https://www.youtube.com/watch?v=0dgh8zSJgO8

IIRC the only options left for DJI Fly are:

1.  duct tape the VPS (optical height sonar / IR VPS)
2. swap to atti mode by sacrificing a mode slot on your controller.
7-28 09:18
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hallmark007
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FriedChicken_II Posted at 7-28 09:18
IIRC the only options left for DJI Fly are:

1.  duct tape the VPS (optical height sonar / IR VPS)

As someone who flies over water on a regular basis, its clear this was clear pilot error and confusion in his explanation . Until we see a flight log we’ll never really know. But it’s unlikely downward sensors were his problem . He mentions his screen went black and he lost VLOS “then it seems strange that knew he was 17 feet above water and to make matters worse he presumed this was ok when simply raising drone another 20/30 ft would have guaranteed safety for his drone as well as helping regain better signal and gps “just another failure”

I fly with vps on and have never experienced problems unless flying below 6ft.

You can see in video below a pure reflection from 6 feet with no problems whatsoever, in fact moving water is more likely to affect vps than still water.

Maybe we might get to see the log someday.

7-28 11:21
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FriedChicken_II
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hallmark007 Posted at 7-28 11:21
As someone who flies over water on a regular basis, its clear this was clear pilot error and confusion in his explanation . Until we see a flight log we’ll never really know. But it’s unlikely downward sensors were his problem . He mentions his screen went black and he lost VLOS “then it seems strange that knew he was 17 feet above water and to make matters worse he presumed this was ok when simply raising drone another 20/30 ft would have guaranteed safety for his drone as well as helping regain better signal and gps “just another failure”

I fly with vps on and have never experienced problems unless flying below 6ft.

Yep, if you fly higher than a safe distance, then no problems at all. IMO the VPS thing only matters when:
1. you were trying to get closer to an obstacle like but actually safe thing like a giant rock that is 1 feet away from your drone. This can happen when you were trying to get a smooth shot from the surface to the beach and then the landscape.
2. you were trying to launch and land the drone from a tiny boat or a small yacht that is swaying a lot making the drone hard to land.

I usually carry a tiny roll of duct tape along with other accessories to adjust for the situation.

7-28 18:29
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kyalami
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hallmark007 Posted at 7-28 11:21
As someone who flies over water on a regular basis, its clear this was clear pilot error and confusion in his explanation . Until we see a flight log we’ll never really know. But it’s unlikely downward sensors were his problem . He mentions his screen went black and he lost VLOS “then it seems strange that knew he was 17 feet above water and to make matters worse he presumed this was ok when simply raising drone another 20/30 ft would have guaranteed safety for his drone as well as helping regain better signal and gps “just another failure”

I fly with vps on and have never experienced problems unless flying below 6ft.

Gi'day Hallamark. Very nice footage with the reflection in the lake of the land and trees and also the mirror of the drone flying over the absolute still water.
7-28 23:52
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hallmark007
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kyalami Posted at 7-28 23:52
Gi'day Hallamark. Very nice footage with the reflection in the lake of the land and trees and also the mirror of the drone flying over the absolute still water.

Hey thank you…..
7-30 18:00
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kyalami
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You are welcome. Just an unrelated question. When I wrote you earlier above it said you were from Sweden and now when I looked you are from United States. How does this work? Have you got a split personality he he he......
7-31 00:37
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hallmark007
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kyalami Posted at 7-31 00:37
You are welcome. Just an unrelated question. When I wrote you earlier above it said you were from Sweden and now when I looked you are from United States. How does this work? Have you got a split personality he he he......

Not sure about US, but last 2 weeks I was over in Sweden visiting my daughter and grandchildren in Uppsala . I’m back in Ireland now, so it should really say Ireland not US.
7-31 04:28
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kyalami
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hallmark007 Posted at 7-31 04:28
Not sure about US, but last 2 weeks I was over in Sweden visiting my daughter and grandchildren in Uppsala . I’m back in Ireland now, so it should really say Ireland not US.

Aha, so it looks like the country shown is determined from where you are when you write a comment or upload a video or picture. Yes this time it says Ireland. Learned something new today. Hope you had a good time in Sweden. At least there was very good weather at that time where you were. Now it will be 20 deg C or under for next 10 days and some rain.
7-31 05:32
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hallmark007
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kyalami Posted at 7-31 05:32
Aha, so it looks like the country shown is determined from where you are when you write a comment or upload a video or picture. Yes this time it says Ireland. Learned something new today. Hope you had a good time in Sweden. At least there was very good weather at that time where you were. Now it will be 20 deg C or under for next 10 days and some rain.

I always have a great time in Sweden thank you and yes the weather was beautiful.
7-31 10:47
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VengefulHemi
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JEZ2 Posted at 5-14 09:12
The Vision sensors are not off over water, but they tend to not work properly.  

Right in your manual DJI recommends flying at least 3 meters over water.  That's a good recommendation if you have a visual on the drone.  Since the altitude is not always perfectly accurate, if for some reason you can't see your drone, I would say you would want more than the 3 meters and would say at least 5 is best so as to not rely on the altitude indicator.

Be very mindful of waves too while close to the water.
8-5 05:33
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Hrodnand
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hallmark007 Posted at 7-28 11:21
As someone who flies over water on a regular basis, its clear this was clear pilot error and confusion in his explanation . Until we see a flight log we’ll never really know. But it’s unlikely downward sensors were his problem . He mentions his screen went black and he lost VLOS “then it seems strange that knew he was 17 feet above water and to make matters worse he presumed this was ok when simply raising drone another 20/30 ft would have guaranteed safety for his drone as well as helping regain better signal and gps “just another failure”

I fly with vps on and have never experienced problems unless flying below 6ft.

And we have a flight log, apparently he was pushing down the left stick withouth noticing, there's still something weird in the log though, there's a sudden altitude drop towards the end, in a split second it goes from 8.9 ft to 0.7 ft and in that moment he wasn't pushing down the stick. Any ideas?




8-11 22:27
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hallmark007
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Hrodnand Posted at 8-11 22:27
And we have a flight log, apparently he was pushing down the left stick withouth noticing, there's still something weird in the log though, there's a sudden altitude drop towards the end, in a split second it goes from 8.9 ft to 0.7 ft and in that moment he wasn't pushing down the stick. Any ideas?

I think that was simply down to VPS not being able to read correct altitude over water and this is explained in the Manual.
8-12 03:14
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