P3 Adv thinks it lower than it is

[9397jim]

Hi, I just got my drone. I took it out today and flew it around 350 yards away slightly downhill. On the iPad screen it said height was 2.8m but it was clearly higher than an old tree behind it. So does the drone take its height from where it took off or does it need calibrated in some way. Thanks, Jim

 

[Steve7777]

Hi, I just got my drone. I took it out today and flew it around 350 yards away slightly downhill. On the iPad screen it said height was 2.8m but it was clearly higher than an old tree behind it. So does the drone take its height from where it took off or does it need calibrated in some way. Thanks, Jim

Yes, the altitude shown is (approximately) relative to the takeoff point, assuming that the home point has been reset.

If you take off and immediately fly down over the edge of a cliff, it will be minus altitude.

I think you would be wise to spend a lot of time reading the downloadable manual from back to front, several times. Phantom 3 Advanced - Specs, FAQ, Tutorials, Downloads and DJI GO - DJI

 

[9397jim]

Yes, the altitude shown is (approximately) relative to the takeoff point, assuming that the home point has been reset.

If you take off and immediately fly down over the edge of a cliff, it will be minus altitude.

I think you would be wise to spend a lot of time reading the downloadable manual from back to front, several times. Phantom 3 Advanced - Specs, FAQ, Tutorials, Downloads and DJI GO - DJI

I will do that, thanks for your help

 

[Fly Dawg]

Also, don't count on that altitude being accurate. Give some wiggle room. I have found, at time's depending on weather conditions, that can vary as much as 10-20 feet. Remember that it only uses a barometer, not an altimeter.

 

[Steve7777]

Also, don't count on that altitude being accurate. Give some wiggle room. I have found, at time's depending on weather conditions, that can vary as much as 10-20 feet. Remember that it only uses a barometer, not an altimeter.

+1 on that - and that's why I said 'approximately'. I can take off and return to near home. I am about 2 metres tall but at my head height the altitude shown in the DJI app can vary sometimes quite a bit from that. The barometer isn't super-accurate - but it's good enough for the job.

 

[Fly Dawg]

+1 on that - and that's why I said 'approximately'. I can take off and return to near home. I am about 2 metres tall but at my head height the altitude shown in the DJI app can vary sometimes quite a bit from that. The barometer isn't super-accurate - but it's good enough for the job.

Much cheaper too! A Predator, it is not.

 

[Richard R]

Also, don't count on that altitude being accurate. Give some wiggle room. I have found, at time's depending on weather conditions, that can vary as much as 10-20 feet. Remember that it only uses a barometer, not an altimeter.

No real distinction between the 2. The altimeter in a manned aircraft is just a barometer with a pointer calibrated to read MSL instead of atmospheric pressure. When I climb into a Cessna, the altimeter has a bladder, gear and lever mechanism, in my phantom, there is a pressure sensitive resistor that is, likely, in a bridge circuit calibrated and with a look up table (or a set of parameters for an equation) to present any imbalance in the bridge as a height. Only difference is than in my phantom, the initial imbalance on start up is the reference from which height AGL is calculated. I doubt that DJI actually calibrates each board but uses a generic data set in the FW. Minor differences in component values or temperature can cause fluctuations in the height reading. Even a flight of a few minutes could cause slight temperature changes which would affect how high the bird thinks it is.

 

[Fly Dawg]

The altimeter in a manned aircraft is just a barometer with a pointer calibrated to read MSL instead of atmospheric pressure.

In that point I was actually referring to a Radar Altimeter.

 

[Richard R]

In that point I was actually referring to a Radar Altimeter.

Got it! Actually, laser rangefinders are small enough that one could comfortably be incorporated into a bird like a Phantom with minimal cost. Would then have a true AGL reading instead of height above Homepoint. Take the sonic sensor out of the VPS and use a Lidar. How cool?