I really like the info at the bottom of the M30T remote controller. It occupy just a small area, but packs in an important information:

• Drone Horizontal and Vertical speed.
• Wind speed and direction.
• Altitude of the drone both above takeoff point, and ASL.
• Distance from the takeoff point.
• Heading of the drone AND direction of the Home Point.
• and even Temprature (I'm not sure if this is measured by the drone or the RC).
  

I wish DJI would include that in the consumer drones Fly App!

That would be really nice if DJI did that.

Especially the altitude above sea level would be very helpful.

ElleKN Posted at 12-6 05:08
Especially the altitude above sea level would be very helpful.

Why is ASL helpful ?

JJB* Posted at 12-6 05:13
Why is ASL helpful ?

During a flight in controlled airspace, the controller sometimes communicates in ASL (QNH).

LV_Forestry Posted at 12-6 05:39
During a flight in controlled airspace, the controller sometimes communicates in ASL (QNH).

do you mean with the controller the DJI RC controller??

No, but ATC asking for a position report.

LV_Forestry Posted at 12-6 07:12
No, but ATC asking for a position report.

Thanks. now i understand.

Don`t think DJI will give an option to enter the QNH in the FlyApp.
But if you know the local QNH and use a hand held barometer, easy to get a correction for the FlyApp baro height.

cheers
JJB

JJB* Posted at 12-6 07:54
Thanks. now i understand.

Don`t think DJI will give an option to enter the QNH in the FlyApp.

You don't need to enter the QNH. Matrice drone gaves the ASL altitude. Most probably from the GNSS, If u-Blox, NAV-POSLLH.  

JJB* Posted at 12-6 07:54
Thanks. now i understand.

Don`t think DJI will give an option to enter the QNH in the FlyApp.

So it is not only a DJI software limitation, but more an hardware choice

JJB* Posted at 12-6 05:13
Why is ASL helpful ?

For example if you are standing somewhere (roof top, riff, tower of a church, montain, ...) and are flying downwards

LV_Forestry Posted at 12-6 07:58
You don't need to enter the QNH. Matrice drone gaves the ASL altitude. Most probably from the GNSS, If u-Blox, NAV-POSLLH.

true, but to compensate small deviations in readings (accurancy sensor) it is handy to adjust the 1013 a little sometimes.
afaik the GPS height accurancy is far from precise....
cheers
JJB

JJB* Posted at 12-6 10:02
true, but to compensate small deviations in readings (accurancy sensor) it is handy to adjust the 1013 a little sometimes.
afaik the GPS height accurancy is far from precise....
cheers

We are talking about GNSS receiver of the enterprise range. When linked to the correction network precision is centimer level.
1013hpa is the standard level, not ASL.
I'm not going to get into a course on altitudes here, there are plenty of them on the internet.  PPL courses are generally very well done to understand.

ElleKN Posted at 12-6 08:25
For example if you are standing somewhere (roof top, riff, tower of a church, montain, ...) and are flying downwards

For example if you are standing somewhere (roof top, riff, tower of a church, montain, ...) and are flying downwards
Knowing your drone's altitude relative to sea level is of no help at all in any of those situations.

Labroides Posted at 12-6 13:23
For example if you are standing somewhere (roof top, riff, tower of a church, montain, ...) and are flying downwards
Knowing your drone's altitude relative to sea level is of no help at all in any of those situations.

Yes it is even dangerous.
I much prefer to have a negative height to realize that the drone is lower than the start point. At altitude ASL it takes time to think about.

When inspecting the flight logs analysis using Airdata, aparently, there is a data generated by the drone, that includes a Barometer Altitude (ie ASL).



There is also an indication of the ASL height at the take off location. This could be acquired by a GPS or a Barometer, but either way, it goes to show that the data is available, and even registered in the log. And if that's the case - why not making that data available on screen...???

Amit Dunsky Posted at 12-6 13:31
When inspecting the flight logs analysis using Airdata, aparently, there is a data generated by the drone, that includes a Barometer Altitude (ie ASL).
[view_image]

Baro Alt is the altitude relative to your take off point. totaly different from ASL.
Example : on take off place, when drone start the pressure recorded = 0m (zero). If you climb the pressure will reduce...altitude rise. It's exponential, do not search a linear relation, 27ft/hpa is +/- true but not exact.

GPS alt : It refere to the ellipsoid. An artificial perfect model of the earth curvature, elevation is given by the GNSS receiver according with Sat signal.

ASL alt : It refere to the seal level, the earth is not perfectly round.

I just check your location, it seems that your software refer to the GE terrain data, exactly 71m at this place, so it is more an illusion of ASL than a true ASL, and totaly independant from the drone.
You can do the test, start the drone on the ground, then re-start it immediatly, to keep the same pressure reference, 1m higher (roof of your car, but do not take off, the compass doesn't like car). I bet your software will still show 71.0m. Instead of 71.0 and 71.1

To summarize, to have ASL with a GPS it is necessary to have a geoid model, or a receiver which directly gives the ASL as the F9P https://www.u-blox.com/en/product/zed-f9p-module.

To have ASL with a barometer, you need a calibrated altimeter, which must receive pressure information, as in airplanes.

DJI consumer drones have neither! They have a simple GNSS receiver GPS+GLO+Beidou+Galileo and a BMP80 type barometer https://www.mouser.fr/datasheet/2/783/BST-BMP180-DS000-1509579.pdf

Amit Dunsky Posted at 12-6 13:31
When inspecting the flight logs analysis using Airdata, aparently, there is a data generated by the drone, that includes a Barometer Altitude (ie ASL).
[view_image]

When inspecting the flight logs analysis using Airdata, aparently, there is a data generated by the drone, that includes a Barometer Altitude (ie ASL).
Not even close.
It's the height you see on your screen.
That's the height relative to the launch point.

Think about it, in the example you showed... you launch and climb to 1 metre (Barometer Altitude) and your drone is 1 metre above where you launched.
Did you launch from the edge of the sea?
Not according to the bit you circled in red.

LV_Forestry Posted at 12-6 10:35
We are talking about GNSS receiver of the enterprise range. When linked to the correction network precision is centimer level.
1013hpa is the standard level, not ASL.
I'm not going to get into a course on altitudes here, there are plenty of them on the internet.  PPL courses are generally very well done to understand.

Thanks, i will do some study on GNSS receivers and their accurancy   ;-)

btw   about 1013 and sea level relation....


cheers
JJB

JJB* Posted at 12-7 00:57
Thanks, i will do some study on GNSS receivers and their accurancy   ;-)

btw   about 1013 and sea level relation....

BTW,

It is exactly what i wrote. 1013 is the standard pressure. It is use for having a perfect model when calculation are necessary, and also for airplanes when they reach the "transition level" to be sure that everyone have the same altitude.

For instance, right now the pressure in Riga Airport is 1004hpa
EVRA 070850Z 15008KT 1600 SN BKN007 OVC012 M02/M03 Q1004 TEMPO 2000


So as describe in the aerodrome chart, the appron altitude is 37 ft. That's mean if right now you set your altimeter to 1004hpa, it will shows 37ft. If you set 1013 it will shows a lower altitude.

I don't know what else to tell you. Download a flight simulator and try!

It is the mention "sea level" which is misleading in the definition of the standard atmosphere. it is science. It's like 1000 liters of water = 1 ton. Yes, but try with sea water you will be disappointed!

LV_Forestry Posted at 12-7 01:10
BTW,

It is exactly what i wrote. 1013 is the standard pressure. It is use for having a perfect model when calculation are necessary, and also for airplanes when they reach the "transition level" to be sure that everyone have the same altitude.

i know this, being a aviation guy

But all this started to be able to inform ATC the ASL height of your flying drone. (your post #6)
If you know the actual height to sea level of your start location and the local air pressure, isn`t it than easy to calculate roughly the ASL height of your drone in the air. As FlyApp shows height relative (minus - zero - plus) to takeoff height.

cheers
JJB