Altitude calibration - when?

[hover.ch]

When does WKM calibrate it's barometric pressure/altitude sensor,
a) only during power-up (that's pretty obvious)
b) during power-up and when setting altitude offset in Ground Station (GS)?

In order to (better) understand how GS deals with altitude/height, this is an interesting detail to know.

 

[FerdinandK]

I think there is no calibration of the baro-sensor, it "just" measures the pressure. The only thing that happens when you set the "altitude offset" is, that a specific pressure is put in relation to a specific altitude, used then for your waypoints. The same happens when the WKM stores it´s "home-point", a specific pressure is stored.

best regards

Ferdinand

 

[hover.ch]

Ok. But the iOSD for example is able to display height in Meter. So there must be a (pretty trivial) calculation of pressure -> height, of course. Hence during power-up, I assume, the current pressure is stored, so that the height can be determined in relation to that pressure / the takeoff point (= 0 Meter).
Do you agree?

My question now is, whether such a reset/recalibrate/pressure recording is also performed when setting altitude offset in GS. I assume it is not because I can't see any communication going on between GS and WKM at this point in time. But I might be wrong.
Can you confirm this?

 

[FerdinandK]

The pressure is put in relation from the height out of the GPS-signal, but I assume you only see the GPS-height info in the OSD. For the altitude offset, the pressure is put in relation to the height info out of google maps (I assume). But I cannot confirm anything, since I have never seen the source-code, ony DJI can confirm. But what problem do you have with it?

best regards

Ferdinand

 

[hover.ch]

..., but I assume you only see the GPS-height info in the OSD.
Ferdinand

I honestly doubt, I'm pretty sure that iOSD's height is derived from barometric-pressure.

My problem is that in GS there is so much magic going on, in respect to height/altitude. I'm supposed do set altitude offset every now and then, without exactly knowing what's going on. Looking at the upload protocol I see Altdiff values I can only guess how they are calculated. That's pretty important because it means that my WP heights are actually modified. As long as I don't understand what DJI/GS actually does, I can hardly tell what's going on (with my MR) and I don't feel comfortable.

 

[FerdinandK]

When I started with the GS, it took me some time, but now, I have the values in the GS displayed as relative height (relative to the starting point). Since at start (and after landing) the copter in the GS displays (relative) height 0, I am happy with it. I also would not care too much what is displayed in the OSD, but what is displayed in the GS is important. But I am sure you can figure this out.

best regards

Ferdinand

 

[hover.ch]

Since at start (and after landing) the copter in the GS displays (relative) height 0, I am happy with it.

Which altitude or rather height display are you referring to?

As far as I know, there are multiple altitude/height values displayed in GS,
- one value "ALTI" value in the header line, right of Lat/Long
- another "ALTI" value in the header line, at the right under Continue/Pause buttons (what is this Alti for?)
- a floating Alti Display (with a yellow border) amongst a set of 4-5 values one can enable or disable in the system settings
- an Altitude indicator/value as part of the instrument panel (I'm using currently instrument panel 1)
- Altitudes of the MR and the WPs on the map

As far as I remember, not all Altidue displays show the same values ...

 

[FerdinandK]

If you have a look here at 1:11
https://vimeo.com/59308284
You see ALTI (which is about 100m) and beside the copter you see also some value around 100m flickering, this is somehow because of the video-capturing, so this is the relative height (relative to the point of takeoff).

The "other" alti-value (below the Continue/Pause) is the RTH-height (20m above the home-point).

best regards

Ferdinand

 

[hover.ch]

I just got a response from DJI concerning the two questions. Instead of an answer, they suggest me to install "GCS 4.0.7 test v3".
No idea why, maybe just one more misunderstanding...

 

[thinwing]

while in gs mode ,my hex obeys all commands except one click takeoff is really scary..it wobbles arround and if terrain is at all rough it will tipp over..man takeoff no prob just power it straight up...2 issue..is while in click and go mode..aircraft travels correctly (both speed and altitude)BUT...once it gets to clicked point it stops and than starts to wobble arround like the auto takeoff and than does a rapid descent to ground!!!...help...it flys normally off the transmitter so I have to save the day by flipping gps mode to man and back again...climb back to safe altitude which it will hold ok...no idea how to trouble shoot this and sent an email off to dji support...anybody else see strange behavior???kpc

 

[gtranquilla]

The hobby altimeter is simply a self-referencing barometer..... It is a simply measures and stores ambient barometric pressure in it's resting state just before launch or take-off then references that to any subsequent barometric pressure during flight.
The difference between the two values is the Altitude above Ground Level, i.e., Altitude AGL and is most useful for RTH since the ground level at the original launch point does not change. Here is an example from an alternate sport...... the documentation for this product explains it well...... http://www.featherweightaltimeters.com/The_Raven.php

The rest related to GCS can get quite confusing and risky especially if you are not taking into account, trees, towers, hills and/or are trying to land your MR on top of a nearby hill........that is why I prefer to fly on a flat are with very few trees.

When does WKM calibrate it's barometric pressure/altitude sensor,
a) only during power-up (that's pretty obvious)
b) during power-up and when setting altitude offset in Ground Station (GS)?

In order to (better) understand how GS deals with altitude/height, this is an interesting detail to know.