Can the altitude AGL update dynamically?

[dannybgoode]

Posting this in general as it applies to at least both my MA and M2P.

So, at the moment if I take off on a hill say and fly straight up to a low altitude - 10m or so and then fly out over the valley Go4 continues to show the altitude as 10m even though it could be much higher.

Is there a way to get the altitude to update in real time. It’s more of an issue when approaching an incline of course. Altitude shows 50m when in fact it’s only 10m and falling...

 

[AeroJ]

In a word, no. Above 10m they have no idea how high they are relative to the ground, and no sensors able to detect that...

 

[dannybgoode]

In a word, no. Above 10m they have no idea how high they are relative to the ground, and no sensors able to detect that...

Thanks for the response.

I just wondered if there could be something in Go4 that would allow the gps coordinates from the drone to pick up the map meta data for altitude. Ok gps altitude data is a bit out but it’s better than nothing.

 

[AeroJ]

I may be wrong (and please someone correct me if I am) but I think it gets the altitude from a barometer rather than GPS...

 

[tcope]

There would also be huge drawbacks. Say you are at 10' and fly over a cliff. The Go app now reports that you are at 200'. You fly around and now want to fly back. You are at 190' above ground level after all. You now crash into the side of the cliff as you are 10' lower.

 

[droneworx]

GPS can calculate altitude, and theoretically, the drone COULD recalculate the altitude, but it doesn't on purpose, its a safety feature. RTH + dynamic altitude would be....a disaster

 

[Meta4]

Is there a way to get the altitude to update in real time. It’s more of an issue when approaching an incline of course. Altitude shows 50m when in fact it’s only 10m and falling...

The problem is in your thread title.
Just as it would be if you were flying a Cessna, the altitude displayed is not an indication of AGL height.
In the Cessna, the displayed altitude would be relative to sea level.
For the drone it's relative to your launch point.

Ok gps altitude data is a bit out but it’s better than nothing.

GPS can calculate altitude, and theoretically, the drone COULD recalculate the altitude, but it doesn't on purpose, its a safety feature. RTH + dynamic altitude would be....a disaster

Does this demonstrate why you don't want to use GPS for altitude?

 

[sar104]

Thanks for the response.

I just wondered if there could be something in Go4 that would allow the gps coordinates from the drone to pick up the map meta data for altitude. Ok gps altitude data is a bit out but it’s better than nothing.

With a digital elevation model, either stored in the aircraft firmware or the app, altitude AGL could easily be displayed either instead of or, better still, in addition to relative altitude. However, it would be of limited use when the altitudes flown are often comparable to the height of obstacles, such as trees and buildings, that would not be accounted for. For flying in mountainous terrain it would certainly be beneficial though.

 

[bushie]

To be usefull would require a huge ammount of memmory to store all the worlds DEM. Also the cost of a sub 1m DEM would increase the cost of your UAV many fold.

 

[sar104]

To be usefull would require a huge ammount of memmory to store all the worlds DEM. Also the cost of a sub 1m DEM would increase the cost of your UAV many fold.

Right, but you wouldn't need to store the entire global DEM any more than you would download and store the entire global map for offline use.

 

[Mr. Salty]

GPS can calculate altitude, and theoretically, the drone COULD recalculate the altitude, but it doesn't on purpose, its a safety feature. RTH + dynamic altitude would be....a disaster

From the Wikipedia article on altimeters:

Global Positioning System (GPS) receivers can also determine altitude by trilateration with four or more satellites. In aircraft, altitude determined using autonomous GPS is not reliable enough to supersede the pressure altimeter without using some method of augmentation.[8] In hiking and climbing, it is not uncommon to find that the altitude measured by GPS is off by as much as 400 feet depending on satellite orientation.[9]

 

[Goin Up]

FWIW, Litchi has a "relative to waypoint" function, which is the closest you will probably get to what you want to do
Litchi relative WP adjustment-1voRnjRuZGI.mp4

 

[droneworx]

From the Wikipedia article on altimeters:

Global Positioning System (GPS) receivers can also determine altitude by trilateration with four or more satellites. In aircraft, altitude determined using autonomous GPS is not reliable enough to supersede the pressure altimeter without using some method of augmentation.[8] In hiking and climbing, it is not uncommon to find that the altitude measured by GPS is off by as much as 400 feet depending on satellite orientation.[9]

you can't really call a drone an "aircraft" in this case for pressure altitude monitoring. Accurate pressure monitoring from pitot tubes are only at about every 1000-1500 feet. Since no one ever really flies a drone above half that height, barometer by itself is not going to be accurate. I had to dig through a manual, but the drones do indeed use barometer and GPS combined to maintain an altitude. So it could recalculate based on absolute or MSL, but there are a lot of reasons why you wouldn't (RTH, not accurate with regard to where you are/were/are going)

from manual

 

[dannybgoode]

You all raise some excellent points that I had not considered.

Makes perfect sense to me now

 

[Lady Rover]

See this thread as well:
Maximum flight altitude limit in mountain terrain?

 

[Meta4]

barometer by itself is not going to be accurate.
I had to dig through a manual, but the drones do indeed use barometer and GPS combined to maintain an altitude.

Correction: The barometer is accurate to less than one foot.
The Mavic does NOT use GPS altitude data at all as it can be +/- 200 ft and more

from manual
View attachment 53317

All that's saying is: If you have no GPS and no VPS, all you have left is the barometer.

 

[droneworx]

Correction: The barometer is accurate to less than one foot.
The Mavic does NOT use GPS altitude data at all as it can be +/- 200 ft and more


All that's saying is: If you have no GPS and no VPS, all you have left is the barometer.

Nope sorry, not even close. Depending on external temperature, baro readiness can vary by over a 1,000 feet, if its not reset through the flight based on local conditions. from a flight training manual.

"On cold and hot days, the actual altitude can be off by hundreds of feet and in more extreme cases more than a 1000 feet. So, if you have a choice in the terrain equipment to use a GPS altitude source or a baro altitude source, I would recommend you set it to GPS altitude. In general, GPS altitude will be more accurate than baro altitude. GPS altitude is affected by the geometry of the satellites overhead, but is unaffected by temperature or pressure and does not need a barometer setting. Standard GPS, non WAAS corrected, vertical accuracy is plus or minus 9 meters, or about +/- 30 feet. GPS altitude is a calculation based on the height above a surface defined by an ellipsoid that models the earth’s shape at sea level. WG84 is the name of the model and is close to a sphere that bulges slightly at the equator. In some places the model is off by small amounts up to 100 feet, but this is corrected for in the GPS by using a correction database."

the Mavic as with all of the advanced drones use a combination of GPS and Baro for measurements, you can argue all day long, but it is what it is.

 

[okw]

Nope sorry, not even close. Depending on external temperature, baro readiness can vary by over a 1,000 feet, if its not reset through the flight based on local conditions.

I'm sure the others in this thread will come along to expand on this, but the Mavic resets its barometric altimeter to zero every time you take off. It's very accurate after that.

Remember, it's only showing the altitude above the take-off point, not above sea level, so calibrating to current barometric pressure is not required.

 

[droneworx]

I'm sure the others in this thread will come along to expand on this, but the Mavic resets its barometric altimeter to zero every time you take off. It's very accurate after that.

Remember, it's only showing the altitude above the take-off point, not above sea level, so calibrating to current barometric pressure is not required.

correct, but thats not what my reply was to. It was to whether the Mavic uses GPS for any kind of altitude and whether barometric altitude is accurate in a commercial aircraft, of which it is, when properly matched as you increase in altitude and waypoints. The barometric on the Mavic is accurate because the altitudes are relatively small

 

[okw]

correct, but thats not what my reply was to. It was to whether the Mavic uses GPS for any kind of altitude and whether barometric altitude is accurate in a commercial aircraft, of which it is, when properly matched as you increase in altitude and waypoints. The barometric on the Mavic is accurate because the altitudes are relatively small

I didn't see anybody else talking about commercial aircraft. But maybe I missed it. Carry on.