400' AGL... off the top of a hill

[Thomas B]

Altitude is set by the aircraft and shown on your controller as height above take off point. NOT above the ground below it. It will not climb or descend related to the ground under it.

Answers to you questions in order you asked:
Yes
No

If you just follow the altitude number on your controller as you try to fly over a slope the peaks at >400 ft (or any flight altitude) you will hit the side of the slope.

 

[AMann]

It's not "following terrain". If the terrain rises 400' your aircraft will strike the terrain. It uses the takeoff point as an absolute reference and knows nothing more.

This is why it would be great to have a display map on the controller display device showing elevation contours.

 

[Starz]

I just watch what the camera is showing me. If I can see the bugs in the top of the trees, I’m to low.

 

[AMann]

I just watch what the camera is showing me. If I can see the bugs in the top of the trees, I’m to low.

What trees? . But really, it would help to keep a constant AGL for mapping, etc., with a M2.

 

[Starz]

Ok. Large bushes.

 

[Drbobk]

Does anyone know why the M2 series uses barometric altimeter readings instead of GPS, which is capable of determining altitude?

And if you then compared the GPS altitude with a topo map, everyone would be happy. You’d have accurate AGL values everywhere you fly.

 

[sar104]

Does anyone know why the M2 series uses barometric altimeter readings instead of GPS, which is capable of determining altitude?

And if you then compared the GPS altitude with a topo map, everyone would be happy. You’d have accurate AGL values everywhere you fly.

The aircraft could use GPS altitude data, which can be quite accurate with good satellite reception, but it's not as consistently reliable as barometric data, which is pretty good for relative altitudes. I'm sure that at some point these aircraft will include digital elevation models, but they don't yet have that. Those models also suffer from resolution issues and lack of information on trees, structures etc. that don't matter much if you are hundreds or thousands of feet AGL, but are often very important at the heights that drones are flown at.

 

[AMann]

Does anyone know why the M2 series uses barometric altimeter readings instead of GPS, which is capable of determining altitude?

Although it is more accurate in measuring latitude and longitude, it is more difficult to get an accurate reading of altitude with a consumer grade GPS, and a barometer is much more accurate and precise than the type of GPS that is in the drone for measuring altitude. One would have to use a much more expensive and larger survey grade GPS and do differential correction to get an accurate altitude reading.

 

[sar104]

Although it is more accurate in measuring latitude and longitude, it is more difficult to get an accurate reading of altitude with GPS, and a barometer is much more accurate and precise than the type of GPS that is in the drone for measuring altitude. One would have to use a much more expensive and larger survey grade GPS and do differential correction to get an accurate altitude reading.

Having run a number of tests on this, in fact GNSS altitude is comparable in accuracy with barometric, and better over significant altitude changes (primarily because the barometric altitude computation has to assume a standard atmosphere) in typical situations where the receiver has a really good sky view, but has lower resolution and stability for small altitude changes.

 

[AMann]

Having run a number of tests on this, in fact GNSS altitude is comparable in accuracy with barometric, and better over significant altitude changes (primarily because the barometric altitude computation has to assume a standard atmosphere) in typical situations where the receiver has a really good sky view, but has lower resolution and stability for small altitude changes.

Precision is the problem- its just not there and a high PDOP really throws it off.

Now if they had put one of these babies on our drones...



I hated lugging one of those around in the mountains in my first FS summer seasonal job!

 

[dsrepairs]

This applies to my experience yesterday. My launch point was about 20' above sea level while filming a regatta. As I moved off the roof over the water the altitude remained the same. I wasn't comfortable dropping down into negative altitude numbers. Could the Mavic 2 Pro go into automatic an automatic landing sequence ?

 

[sar104]

Precision is the problem- its just not there and a high PDOP really throws it off.

The PDOP is generally very good though. It really needs a careful consideration of the source of both the random and systematic errors in the two methods to get a meaningful comparison. GNSS has little or no systematic error, and random error that changes on the timescale of minutes as the constellation moves (DOP). Barometric relative altitude has a variable systematic error that depends on the deviation of the atmosphere (temperature and density) from the standard atmosphere, and potential pseudo-random error on a timescale of tens of minutes as the atmospheric conditions change. I think that's the main reason that barometric is regarded as more robust for short flights.

 

[sar104]

This applies to my experience yesterday. My launch point was about 20' above sea level while filming a regatta. As I moved off the roof over the water the altitude remained the same. I wasn't comfortable dropping down into negative altitude numbers. Could the Mavic 2 Pro go into automatic an automatic landing sequence ?

The aircraft will not autoland just because the height relative to takeoff is negative. That's not a factor in the autolanding process.

 

[Meta4]

Could the Mavic 2 Pro go into automatic an automatic landing sequence ?

Fortunately the DJI designers imagined that (just like a real plane) there could be situations where a drone is flown from a high point down to lower altitudes.
It makes no difference to the drone whether the altitude has a + or - in front of it.

 

[GB1Yorkshire1]

Or a sticky with a link to the manual?

Then owners would have to READ the manual!!
What next..... understanding FAA regulation?

 

[Waynebru]

Attached is a video I shot a year ago. It is a hill above La Jolla (suburb of San Diego) Notice that I got about 100 feet above the monument. I went back a month ago and now the drone won't go higher than 15 feet. That's because of Miramar Air Base a few miles away. The hill is in the path of the runway and has a 400 foot ceiling.

 

[Thomas B]

Attached is a video I shot a year ago. It is a hill above La Jolla (suburb of San Diego) Notice that I got about 100 feet above the monument. I went back a month ago and now the drone won't go higher than 15 feet. That's because of Miramar Air Base a few miles away. The hill is in the path of the runway and has a 400 foot ceiling.

What is the elevation of the top of the monument?

 

[kadras]

I went back a month ago and now the drone won't go higher than 15 feet. That's because of Miramar Air Base a few miles away. The hill is in the path of the runway and has a 400 foot ceiling.

Your problem is DJI, not Miramar. The extension of the Miramar runway over Mt Soledad is a DJI restriction, which you can fly in by getting permission through DJI. The FAA maps show no restrictions over Soldedad, but that is crowded airspace with fast movers from Miramar, other aircraft from Montgomery and the coastal flyway. There is a 400 ft ceiling for all sUAS recreational flights.
Here is the FAA Facilities Map

The FAA TAC chart which shows Class B airspace from 4800 to 10,000.

The DJI map

The FAA VFR Fly Map

 

[bobscheel53]

yes i'm probably confused on this. it's 400 ft agl. got it.

so help me understand, what does "400 ft agl off the top of a hill" means? does that mean you're at 400 agl while you are on the top of the hill?

eta: never mind, got it. had to keep re-reading it. it's flat here, we don't have hills. op said he took off and went all the way up to 400 agl and the moved off. ok.

You must remain within 400 ft of the ground when moving away from the hill. If the hill is more like a cliff, 400 ft from the side of the cliff is acceptable.

 

[kensteele]

this is al

You must remain within 400 ft of the ground when moving away from the hill. If the hill is more like a cliff, 400 ft from the side of the cliff is acceptable.

oh ok, that makes sense. i thought you might have had to lower the drone to stay acceptable. again, it's all flat around here so won't have that problem but good to know. i bet only 1% of recreational drone flyers will ever know this.