Take off and Landing Heights

[Lets Fly]

I only just noticed that the height you take off from is 0 feet, but the height when you land is a minus the feet height of when the home point was remembered.
Is this a common thing to happen? Its not always exactly the same footage, but still minus.

 

[steve_lyt]

what can happen is that the heght it shows is gps so if the land is sloping it can be a negative number compared to the take off height

 

[Lets Fly]

what can happen is that the heght it shows is gps so if the land is sloping it can be a negative number compared to the take off height

No, its a flat parking lot in Florida no less.

 

[dawgpilot]

I only just noticed that the height you take off from is 0 feet, but the height when you land is a minus the feet height of when the home point was remembered.
Is this a common thing to happen? Its not always exactly the same footage, but still minus.

I suggest not taking off before the home point is set. It's a good way to lose your drone if something goes wrong with your connection.

 

[Lets Fly]

That me be, but I was under the impression that the drone recognized the ground from a photo memory at a height of maybe 15 feet, not so?
Plus when you go straight up and wait for home point to record, the GPS should be the same.

 

[steve_lyt]

check the log if you can, and check if home point was recorded

 

[Lets Fly]

Yes it was that's how I first noticed it. I went to several videos and played them back and stopped them when home point was recorded and checked the height. Then I went to the landing and watched as the height goes below 0 to minus so many feet and as I said
it does not always match the home point height. For instance on one, the home point recored at +14 feet, and when landing it was right at -14 feet. On another the home point recored at 12 feet and when landing it was at -6 feet.
I just went back and checked some flights from a year ago, and one took off from 0 and landed at 0, another took off and recored home point at +6 feet and landed at -6 feet. So, apparently it has happened all along and I had not noticed it,
and it may not be a problem. In my year and a half of flying the MA I have had zero problems with it, but was wondering why this should occur. Must be just the GPS signal transfer somehow.
Fly safe.

 

[old man mavic]

when the drone is under a certain height it uses the sensors under the drone to know its height, when you then go up the barometer takes over, and this can fluctuate quite considerably due to changing air pressure as it flies, it is not an absolute figure, and also remember that the reading being sent from the drone to the display has a slight delay between the actual height, and what is displayed on the screen, the readings are a bit like the fuel gage in a car they are not really that accurate either

 

[Lets Fly]

when the drone is under a certain height it uses the sensors under the drone to know its height, when you then go up the barometer takes over, and this can fluctuate quite considerably due to changing air pressure as it flies, it is not an absolute figure, and also remember that the reading being sent from the drone to the display has a slight delay between the actual height, and what is displayed on the screen, the readings are a bit like the fuel gage in a car they are not really that accurate either

Makes sense, thanks Old Man, although I may be older than you, Ha Ha. Scratch that, I just saw your age, you got me by 3+.

 

[Meta4]

I only just noticed that the height you take off from is 0 feet, but the height when you land is a minus the feet height of when the home point was remembered.
Is this a common thing to happen? Its not always exactly the same footage, but still minus.

Your question is a little sketchy but maybe this is what you are asking about?
The height data comes from a barometric sensor and changes in air pressure during the flight often cause differences of a few feet so that the landing spot reads as +/- a few feet at the end of the flight.

 

[Lets Fly]

Your question is a little sketchy but maybe this is what you are asking about?
The height data comes from a barometric sensor and changes in air pressure during the flight often cause differences of a few feet so that the landing spot reads as +/- a few feet at the end of the flight.

Not sure what was sketchy, just asking why the difference between take off and landing heights. If its barometric pressure readings showing the differance, sounds reasonable. Thanks.

 

[Mboy]

Following on from this, if I take off from a cliff overlooking a river valley, and the drone descends into that valley, will the onboard system for registering the T/O point cope? That is, I'll be flying below T/O, in negative altitude as far as the drone is concerned. If I hit RTH, it will come back to the T/O point?

 

[Thomas B]

Following on from this, if I take off from a cliff overlooking a river valley, and the drone descends into that valley, will the onboard system for registering the T/O point cope? That is, I'll be flying below T/O, in negative altitude as far as the drone is concerned. If I hit RTH, it will come back to the T/O point?

Yes. It will ascend to the RTH height relative to TO point and return there.

 

[old man mavic]

just be aware that as the drone gets closer to the home point ,then it will be subject to the updraft and varying levels of wind direction that can happen in a valley ,which can impact on its ability to get back, just allow a bit of extra remaining battery charge for the homewards journey .it will be using a lot more battery to fly back as it ascends ,than it did on the way down and out from the home point