As it must use GPS for distance from the home point. This would avoid the problem discussed elsewhere of flying at an illegal height when flying from a hill over a valley or indeed apparently exceeding the legal height when trying to fly over rising land from a valley. Surely with all the other amazing functions programmed into the firmware this should be a doddle. Am I missing something or is this not desirable?
Why doesn't a drone use GPS for legal height rather than home point height
- Thread starter scubadesflier
- Start date
1. GPS wouldn't give you the height above the ground below the drone.
That's not something that GPS can do.
It would give an (inaccurate) height above sea level
2. GPS altitude isn't very good anyway.
There is no sensor that's small enough or cheap enough to do what you are asking for.
The pilots of most real general aviation aircraft don't have agl height either and use a barometric sensor just like your drone.
Given a good idea of the drone's height relative to the home point it's not hard to estimate agl height.
If it's really an issue where you are, do a little research of local altitudes with a topo map or Google Earth to help even more.
Height above ground is not a good indicator of the presence of obstacles.
I'll clarify my statement because I'm always thinking BIG.
That's not clarification, it's only repetition.
"One day when AI becomes a real thing in drones ..."
"At that point when AI becomes a real thing in drones ..."
No matter how powerful it is, AI will never be able to identify and avoid obstacles based on absolute height above ground. Which of these two drones is in distress?
(Image generated with AI and Photoshop.)
Last edited:
Of course it won't, only an idiot would try to use AI to identify and avoid obstacle based on absolute height above the ground. Not sure where you got that method from but anyway, come over the AI forum where you can open your mind, use your imagination, and think outside the box, and we'll teach you how it can be done. We don't use the term "no matter how powerful it is..." and "never."
Your word.
See post #3.
"One day when AI becomes a real thing in drones, there won't be a single spot on the planet where your drone can exist that cannot be determined how high about the ground below your drone is flying. At that point, obstacle avoidance will be obsolete."
You misunderstood.
OA will be obsolete in drones when real AI becomes a thing with drones. Period.
Maybe you can stop nitpicking.
It seems that three other folks read your post the same way I did. No nits picked. Just a response to a non-sequitur.
On a more interesting topic, how would AI eliminate the need for obstacle avoidance? Isn't it more likely that it could lead to more effective obstacle avoidance functions rather than eliminating the need for OA?
Fine to initially read it that way; got it. Not so fine after I already explained what I actually meant. Three other people didn't actually post they thought it was a serious interpretation *after* I made it clear.
Think outside the box.
anotherlab
Well-Known Member
Exphantomflyer
Well-Known Member
Seeing as how the max height allowed is taken from zero feet at point of take off, flying from a hill still allows you to be 400ft above it, if you fly over a valley the height is taken from take off point, even if the land dropped 1000ft below you, you wouldn't technically be flying below max height if you are at 350ft even though over the valley the quad would be at 1350ft.
Im guessing that aircraft flying over land at a set height will automatically adjust their height based on land topography so you would always be safe.
Here's a theoretical solution...
GPS is quite accurate in determining horizontal location, but not so much for vertical. And, as others have pointed, even if it was accurate enough, GPS would only tell you your height above sea level. So you'd also somehow need to know the actual sea level elevation of the terrain currently below the drone in order to calculate the actual height above ground.
Large airliners have radar altimeters which, when within range during landing or takeoff, bounce a radar signal off the terrain below. Similar to DJI's VPS sensors, those provide a very accurate above ground level (AGL) measurement, but they have limited range. (And in the case of radar altimeters, they operate close to 5G frequencies, which is why you're asked to turn off your cellphones!)
Within Google Earth, you can place your screen cursor over any point on Earth and it will display that location's height above mean sea level (MSL). That data actually does exist. However, that huge database is stored on Google Earth's server and only a tiny portion is downloaded for the bit of the map currently showing on your browser's screen.
There's no way that DJI's drones will have enough internal onboard memory capacity to store the entire enormous database in sufficient detail for the entire Earth. But, couldn't you pre-load similar terrain MSL elevation data the same way you preload pre-flight satellite-view map data?
If you could download the terrain elevation downloaded for just the map area you intend to fly in, you wouldn't need to rely on active inaccurate GPS height measurement. Your relative height is still zeroed using the barometric altimeter at your take-off location. As long as you wait long enough to obtain a good GPS lock and have your Home location matched to that take-off location, your drone should then know and record the terrain MSL height of your take-off location.
Thereafter the drone could look up, within it's downloaded terrain elevation data, the MSL elevation of any current GPS location during it's flight. Knowing that, it can calculate it's actual height above ground level (AGL) relative to its take-off location, plus whatever height its more accurate barometric altimeter is currently reading.
That's the problem though. That's only allowed if the terrain is completely flat.
The regulations refer to a 400ft limit above ground level. Currently, DJI drones can't tell you how high they actually are above ground (unless within range of the VPS height sensor).
The displayed height is always referenced back to zero at take-off location. So if the drone's barometric altimeter is showing 350ft height when you fly off a 1000ft cliff, your display continues to show only 350ft height even though the drone is actually now 1350ft above ground, which is illegal.
The drone only knows what the barometric altimeter is registering, so it thinks it's only 350ft high. It's the pilot's responsibilty to know the actual height of terrain features in order to keep the drone within the 400ft legal AGL height.
Sophisticated modern fighter jets, and cruise missiles, have terrain following capabilities based on stored elevation maps.
General aviation aircraft use barometric altimeters, which need to be calibrated to local ambient barometric pressure settings (which vary with weather conditions) in order to display altitude relative to sea level.
Back when I was still flying out of St.Catharines Airport (near Niagara Falls), the plane's altimeter setting had to be adjusted so that it read 325ft when sitting on the ground at the airport, as that is the MSL elevation of that airport.
You are completely wrong in this.
The height you see on your screen is relative to where you launch, but it would be ridiculous for regulations to be.
Perhaps this helps understand why:
As post explained, no .. civilian aircraft don't do that.
Exphantomflyer
Well-Known Member
You are completely wrong in this.
The height you see on your screen is relative to where you launch, but it would be ridiculous for regulations to be.
Perhaps this helps understand why:
As post explained, no .. civilian aircraft don't do that.
Thats incorrect, taking off from B would put the drone at 500ft, taking off from A would put the drone at 100ft,
The drone sets the height to zero from take off point hence why you can still fly at 400 ft max from point A
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