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nigelw
First Officer
Flight distance : 518084 ft
United Kingdom
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During low level flights with VPS switched on, you get 2 different height readouts in the Go app.  One from the barometer & one from VPS.  If I'm flying at say 2 metres, shouldn't they both be reading the same?  Doesn't one correct the other?  I don't normally have VPS switched on so I don't know what's normal.
2016-4-4
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dji-p3p1
Second Officer
Flight distance : 534970 ft
Australia
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Hey Nigel.

I haven't noticed that. I'll try and check it out tomorrow morning.
2016-4-4
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nigelw
First Officer
Flight distance : 518084 ft
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dji-p3p1 Posted at 2016-4-4 14:03
Hey Nigel.

I haven't noticed that. I'll try and check it out tomorrow morning.

Thanks

I would expect VPS to take precedence, otherwise what's the point of it?
2016-4-4
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jaycee
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If you are flying 3 meters or less over ground that is a different elevation than your take-off point,  the two readings should be different.

VPS should be more accurate, but its not perfect.

It projects sound waves downwards and waits for the resulting echo to calculate its distance from the ground. If the phantom is over tall grass, thick carpet, water or other sound absorbing material, or if its moving fast enough that it has to tilt and project the sound waves above a certain angle, the system becomes un-reliable.

Cheers
2016-4-4
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nigelw
First Officer
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United Kingdom
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jaycee Posted at 2016-4-4 16:42
If you are flying 3 meters or less over ground that is a different elevation than your take-off poin ...

Yes, I understand how it works & agree the sonar part of VPS should be more accurate.  But why would you ever have different readings?  If the display shows 2 different altitudes, which one is relevant?  There seems little point in showing a second altitude if it's not being used for anything.

Is it used for low-level waypoint missions for example?  I read earlier on a P4 thread that the aircraft will follow the ground contours, but I've not heard of this before.
2016-4-4
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Kneepuck
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nigelw Posted at 2016-4-4 08:54
Yes, I understand how it works & agree the sonar part of VPS should be more accurate.  But why wou ...

It's because the Barometric altimeter,  in order to be accurate,  would need pretty much constant calibration,  just as the ones in the large aircraft do.Weather conditions, temp, etc affect atmospheric pressure and that is what the Phantoms use to determine altitude.  So for it to be accurate,  we would need a way to calibrate it.  It is not that sophisticated. It just records the reading at startup and uses that for a baseline.  Temp changes,  pressure changes it records as altitude changes even if the P3 is just sitting on the ground.  And for VPS to be perfectly accurate would require perfect conditions as well.  Thus, we as pilots have to consider all this stuff all the time.  Maybe one day we will get radar altimeters. Until then.....
   
2016-4-4
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nigelw
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Kneepuck Posted at 2016-4-4 19:13
It's because the Barometric altimeter,  in order to be accurate,  would need pretty much constant  ...

I also know how a barometer works, that's not what I'm asking.

I really don't see any advantage in having sonar if all it's going to do is display a different height.  What use is it?  If the aircraft or pilot doesn't know which is correct, it just adds to the confusion.
2016-4-4
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Kit Walker
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Australia
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nigelw Posted at 2016-4-5 05:59
I also know how a barometer works, that's not what I'm asking.

I really don't see any advantage i ...

Lol, I wondered the same thing.
I understand how they work also, but wondered why they don't help each other out.

I.e.  When reading 10m high.., but really only 2m off the ground.., perhaps VPS could help the barometer.
2016-4-4
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Kneepuck
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nigelw Posted at 2016-4-4 12:59
I also know how a barometer works, that's not what I'm asking.

I really don't see any advantage i ...

Ya,  that's true.  But,  despite what Dji says,  my experience is that the vps is more effective at holding horizontal position than vertical. And even at that, the horizontal position has a good deal of drift to it.  Over an optimum surface at 4 or 5 feet,  I still see my P3 wandering around within a couple of square foot box.  It would be really awesome to have a radar altimeter module we could install. That would be a game changer in many ways.
2016-4-4
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Kneepuck
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Kit Walker Posted at 2016-4-4 17:06
Lol, I wondered the same thing.
I understand how they work also, but wondered why they don't help  ...

I think even Dji knows that the accuracy of either one is not precise enough to be used to correct the other
.
2016-4-4
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raveneapoe
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nigelw Posted at 2016-4-4 11:54
Yes, I understand how it works & agree the sonar part of VPS should be more accurate.  But why wou ...

The VPS registers the height of the Phantom no matter where it is at the time, a more or less real time, actual height.   The barometer is calibrated to the take off point only.
If you take off at one point, and fly low up the side of a hill, the barometric measurement will say (for instance) 150 feet, while the VPS may say the more or less actual height above the actual surface the Phantom is flying over on the hillside,  (for instance) 6 feet.

And, of course, barometric pressure measures air density which can change due to weather conditions.
2016-4-4
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C_LUU
Second Officer
Flight distance : 481988 ft
Australia
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nigelw Posted at 2016-4-5 03:59
I also know how a barometer works, that's not what I'm asking.

I really don't see any advantage i ...

The point was so we could fly our phantoms inside and under cover with out GPS. Unfortunately VPS never really lived up the some of the hype, readings were inconsistent and patterns on the ground needed to be very clear and easy for the P3P to determine. This resulted in most users turning VPS off.
2016-4-4
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quaddron3
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Canada
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Kneepuck Posted at 2016-4-4 20:44
Ya,  that's true.  But,  despite what Dji says,  my experience is that the vps is more effective a ...

My VPS is better at holding vertical position than horizontal indoors. The VPS is actually horrendous because it drifts all over the place. And i usually fly where there is direct lighting above, so I think the p3 is chasing its own shadow.  It would stay still for a while, then once it drifts a little bit, it starts accelerating and chasing its shadow.

The VPS has another annoying feature which is when you land, you have to be very decisive about continuing to push the joysticks down, because after a while they go full thrust automatically to lift the bird back up. So if you're doing a controlled slow landing, well you can't. Do it faster because the upward thrust will turn on when its really close to the ground.

I find turning VPS off makes for easier controls indoors.
2016-4-4
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FatedFilmsNC
Second Officer

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quaddron3 Posted at 2016-4-5 02:08
My VPS is better at holding vertical position than horizontal indoors. The VPS is actually horrendo ...

how do you turn VPS off?
2016-4-5
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FatedFilmsNC
Second Officer

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i actually ran backwards into a tree the other day and bent one of my sensors...and now i'm getting the hovering around in a little 3x3 box instead of an even hover. Also, the P4's readings of how far I am off the ground are not correct anymore. **edit** only when im 10m or closer to the ground.

Bent Sensor P4

Bent Sensor P4
2016-4-5
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Kit Walker
lvl.4

Australia
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My VPS will kick in around 2m. Just thinking that is close enough to 2m.., that it could reset the barometer reading which may read several meters
2016-4-5
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quaddron3
lvl.3

Canada
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FatedFilmsNC Posted at 2016-4-5 05:05
how do you turn VPS off?

You can do that in the settings.

I turn it off indoors. Outdoors its back on.
2016-4-12
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FatedFilmsNC
Second Officer

United States
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quaddron3 Posted at 2016-4-13 11:43
You can do that in the settings.

I turn it off indoors. Outdoors its back on.

Where in the settings? I do not see it in there anywhere.
2016-4-13
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quaddron3
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Canada
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FatedFilmsNC Posted at 2016-4-13 14:34
Where in the settings? I do not see it in there anywhere.

Wait, are you an owner of P3 or P4?

P3 you can turn off.

I don't own the P4. I heard you CANNOT turn off VPS.
2016-4-14
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Kestrel Aerial
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quaddron3 Posted at 2016-4-14 19:43
Wait, are you an owner of P3 or P4?

P3 you can turn off.

According to the P4 manual VPS only works from 0.3 - 3.0 meters. What's not in the manual is ANY FLIPPIN THING ABOUT THE BAROMETER. So if anyone can clarify for me. My take-off altitude was 2093 ft, at the first waypoint setting of 50' the SRT file indicated and Barometer of between 14.9 and 15.8 (multiple filights). On one flight I landed the aircraft at a published 2185'. The barometer reading was 33.2  If anyone who knows how to read this to get the altitude Please let me know. Thanks!
2016-5-24
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labroides
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Flight distance : 9991457 ft
Australia
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Kestrel Aerial  Posted at 2016-5-25 10:28
According to the P4 manual VPS only works from 0.3 - 3.0 meters. What's not in the manual is ANY F ...

Your post is a bit confusing.
Are you saying that your Phantom showed a difference of 33.2 for a height difference of 92 feet?
If so it sounds like you have your app set to display metric units and it's indicating a height difference of 33 metres?
That's pretty close to correct and given uncertainties in the map elevations you've used it may even be accurate.

If your height data is a bit off try recalibrating the IMU and see if that corrects it.
2016-5-24
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Kestrel Aerial
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Kestrel Aerial  Posted at 2016-5-24 20:28
According to the P4 manual VPS only works from 0.3 - 3.0 meters. What's not in the manual is ANY F ...

Well I finally pulled my head out of _ _ and answered my own question. And I did find one mention about the barometer. It only is used when you're flying ATTI mode.
2016-5-24
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labroides
Captain
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Australia
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Kestrel Aerial  Posted at 2016-5-25 10:55
Well I finally pulled my head out of _ _ and answered my own question. And I did find one mention  ...

No ... the barometer is the primary altitude sensor and it's used in all modes
2016-5-24
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Kneepuck
Captain
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Kestrel Aerial  Posted at 2016-5-24 17:55
Well I finally pulled my head out of _ _ and answered my own question. And I did find one mention  ...

I think you mis read that.  The barometric altimeter is always used.  But in atti mode,  ONLY the barometric altimeter is used for altitude holding.  No position hold available,  only altitude.
2016-5-24
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labroides
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Kneepuck Posted at 2016-5-25 16:16
I think you mis read that.  The barometric altimeter is always used.  But in atti mode,  ONLY the  ...

Except for VPS at low altitudes, there is no other source of altitude data.
The barometer is the primary altitude sensor.
2016-5-24
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Kneepuck
Captain
Flight distance : 275102 ft
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labroides@yahoo Posted at 2016-5-24 23:19
Except for VPS at low altitudes, there is no other source of altitude data.
The barometer is the p ...

Quite correct
2016-5-24
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