I wonder what can the reason be?
I was getting ready for a 3 mile mission, but I like to test it hovering and flying around for 1-2 minutes first.

Today I noticed that it was not hovering smoothly.  It was like dancing left leg up then rght leg up.  Like a little woble.

I flew around with no issues, but I get concerned when I see changes; so I decided to re-calibrate it later today (IMU, Compass) and try again tomorrow.
I had calibrated everything last week.

It was not very hot, it was about 81 degrees and not too humid outside.

Has anyone seen this behavior?

Sorry, not too many may know what boogie down was.

The dance was similar to Drop it low:

Hello MD_Icarus, any video clip of this issue will be appreciated.

I calibrated the IMU/compass and I tested it today and it seems fine.   But I wil be testing it in the same area the issue was observed later.

In that area, it hovered above tall 4 ft beach grass with a slight cross wind.  There is always cross winds there.  Would the tall grass and wind "confuse" the sensors?

Hello.
I would say if the drone "see's" the ground moving (gras in the wind) it will try and adjust for that.

4 feet is pretty close and I would think that the moving grass has some effect on the drone.

When this happens next time try to hover a little higher and see what happens.
I would think that it gets better with distance (up to 10 meter I believe).

You should be fine.

I thought the same thing after I watched the video and I observed the tall grass move around with the wind.

But I had it up about 7-15 feet though; the grass was about 4 feet tall.
I flew it in a different area today with no issues at all.  I will try the tall grass area in a few days.  I will post a video once I complete the editing.

rainer1 Posted at 2016-7-20 20:19
Hello.
I would say if the drone "see's" the ground moving (gras in the wind) it will try and adjust ...

I totally agree with rainer1. My drone will have a small "dance" now and again when hovering a few feet over grass ESPECIALLY when there is cross wind. The damn wind always decides to pick up as I come in to land on soft grass lol. Just hold it above landing spot till crosswind disappears, drone settles from "dancing" then a nice soft landing.

Nothing to worry about IMO.

MD_Icarus Posted at 2016-7-20 17:34
I thought the same thing after I watched the video and I observed the tall grass move around with th ...

The VPS of Phantom 4 works below 10 meters, or about 33 feet. So it detects the grass is swinging and thought itself was blowing away by wind.

The interesting thing is that if you try to land Phantom 4 on a moving ship's deck, it will move with the ship in absolute speed and hover still on the deck, if the deck has clear patterns for VPS to detect.  edit: Only when not enough GPS is not available.

DJI-H.C Posted at 2016-7-21 05:13
The VPS of Phantom 4 works below 10 meters, or about 33 feet. So it detects the grass is swinging a ...

I did not know that.

I thought GPS lock is the primary control, and VPS the secondary.
I thought VPS was for altitude control only, and GPS was still the primary position lock. (The moving grass was below the P4)

How does GPS and VPS work together then below 10 meters?

MD_Icarus Posted at 2016-7-22 06:18
I did not know that.

I thought GPS lock is the primary control, and VPS the secondary.

Sorry, I just checked it, the case landing on the ship was when not enough GPS signal is available.  GPS indeed has higher priority over VPS.

I am not 100% sure but I would think that gos is not used for landing.
GPS shouldn't be even close enough to be considered.
I just can't see that the altitude calculation from the satellites is so good.
Maybe up to a few feed, in civilian use.
Just not good enough for landing.

I think GPS is used to maintain the horizontal position at any altitude.  You can see the difference as soon as you go into ATTI mode, even when you fly 3 feet over the ground, it starts drifting with the wind. (GPS is off).

I am not sure if DJI uses differential correction using the user's device which is at the ground, but even with no such correction, it can be accurate to within a few feet, assuming you have a large number of satellites (the more satellites, the less error).

I think it uses GPS to maintain horizontal position during landing, and the VPS is used to control vertical position.

MD_Icarus Posted at 2016-7-22 14:31
I think GPS is used to maintain the horizontal position at any altitude.  You can see the difference ...

indeed very similar, except very short grass when I experienced this, perhaps so short that VPS couldn't differentiate a pattern and thought it was on a snooker table :p

Just good to know, and learn of all possibilities and variables

I think its the Sonar to adjust height up to 10m , and the two cameras assist with the horizontal hovering position. As mentioned grass or sand, or similar surfaces with no obvious pattern makes things difficult for the cameras to lock onto.

Simple test. Go back to same location, verify problem still exists, then shut of the positioning system in the Go App and try again. If it is the positioning system (which makes sense to me given the conditions), it should not do it then. In fact you should be able to shut it off while hovering and see the change immediately.

KM5RG-Robert Posted at 2016-8-14 17:28
Simple test. Go back to same location, verify problem still exists, then shut of the positioning sys ...

Except that on a P4 you cannot shut off VPS in DJI Go.

Aardvark Posted at 2016-8-14 20:49
Except that on a P4 you cannot shut off VPS in DJI Go.

And where it can be done?

dr_noise@mail.r Posted at 2016-8-14 19:04
And where it can be done?

On a P3 you can chose to turn off VPS, this option is not available on the P4.

Edit:- Or at least not using DJI Go...

Did not know that. Wonder why the difference?

KM5RG-Robert Posted at 2016-8-15 07:34
Did not know that. Wonder why the difference?

Don't know, it has not been explained by DJI and when the question has been asked, there was no answer forthcoming.

There is a solution tho, not tech savy, but proven to work in some cases, put tape over the sensors... in this video a guy does this to stabalize his drone over water, rather then have it follow the current

So it looks like it ignores the GPS in favor of the positioning sensors which is not what I read earlier according to DJI. There needs to be a (more elegant) way to shut them off for the P4 then.