Can someone explain the height sensors of the Mavic for me , I have a quick diagram to help explain what I mean

if I take off and go 400 ft. (120m Max height in the uk ) from point a on top of a hill then fly to the next hill but the land fall away making the gap to the ground 500 feet will the Mavic descend to 400 feet from the ground its now above or stay at 500ft?

In my video below I did this but did not see the height go below 400ft on the screen and when I got over the next hill it was saying 400ft but it was nowhere near 400 ft. above the ground


So over hilly ground how do you know how high you are at any point ? and what about if the next hill is above the 400ft where you taken off from ( point C )

Hope someone can clear this up for me ...

No, it won't automatically adjust its altitude up or down: the pilot is responsible for that. And regardless of any adjustments you make, the value that's displayed is the estimated height relative to your takeoff point -- and can even be negative if, for example, you take off from the top of a hill and fly into a valley or other area of lower elevation.

The Mavic uses multiple sensors, in differing importance, throughout your flight.

Only GPS is external to the Mavic. All other sensors are internal and self-contained within the Mavic. GPS altitude, measured as Above Sea Level (ASL) is acquired and use but tends to be less reliable than the internal sensors of the Mavic over the dynamic flight envelope of the Mavic.

So as you takeoff, the Mavic uses VPS to stabilize the aircraft. VPS is very similar to the radar altimeter on piloted aircraft - very accurate within 43 feet of the ground - but measures the relative distance above the ground or obstacle (AGL). The Attitude and Heading Reference System (AHRS) sensors, which include IMU gyros & accelerometers biased with compass and barometric altimeter are far more accurate than GPS altitude but again measured in AGL. So the primary altitude reference in the Mavic is always referenced relative to your takeoff location and is displayed as a differential above or below that takeoff spot, (+/- AGL).

So in your scenario, the Mavic is measuring realtime rate of change, biasing the barometric altimiter, to show the altitude differential between your takeoff spot altitude and the current aircraft altitude. It could care less about the terrain below it. If you decend into the valley, at 100 feet above the terrain, the altitude will show 0, go 25 feet lower and the alttude will show -25 feet as you are 25 feet BELOW your takeoff point.

If you climb back to 400 feet and proceed to point C, you can crash into the hill. But three systems, if enabled can protect you. The first and most important system is visual Line of Sight (LOS). See the hill and avoid it. With distance, depth perception becomes your enemy. So you should perform some risk assessment before each flight and know the obstacles, know their height, know the safe minimum altitude and set your RTH height.... The other two system are Mavic systems -> obstacle avoidance and VPS. At 43 feet above the rising terrain, the VPS system should start to show the VPS altitude and show it decreasing. If obstacle avoidance is enabled, it should stop the aircraft if and when it identifies an obstacle like the hill.

Very complete explanation, Daroga.

DroneFlying Posted at 2017-4-3 06:00
No, it won't automatically adjust its altitude up or down: the pilot is responsible for that. And regardless of any adjustments you make, the value that's displayed is the estimated height relative to your takeoff point -- and can even be negative if, for example, you take off from the top of a hill and fly into a valley or other area of lower elevation.

Wow what did it take you all of a minute to write that? just incase no one else says it but the reply came across with a hint of arrogance to it. It was a valid question and one that was answered in detail by another forum user that has cleared it up for the original OP.

Thank you , well expand and its all relative to your take-off location something to thing about next time I go out over the hills

SamBGB Posted at 2017-4-3 06:45
Wow what did it take you all of a minute to write that? just incase no one else says it but the reply came across with a hint of arrogance to it. It was a valid question and one that was answered in detail by another forum user that has cleared it up for the original OP.

Wow what did it take you all of a minute to write that?

What does the length of time it took me to reply have to do with anything?

just incase no one else says it but the reply came across with a hint of arrogance to it.

It wasn't intended that way, but I suppose arrogance is in the eye of the beholder. In any case, it's not your place to decide what is or isn't appropriate on this forum. And what did your own post add to the discussion besides hostility? Maybe you should spend more time examining your own attitudes than guessing at those of others and lecturing them about it.

It was a valid question and one that was answered in detail by another forum user that has cleared it up for the original OP.

Yes, it was a valid question and I never said or implied otherwise. And yes, Daroga's answer was much more in-depth than mine.  I generally try to keep my answers short because I know many people prefer it that way and sometimes won't even read long ones. The OP asked if the Mavic would adjust its height automatically and I gave what I did -- and still do -- consider to be a reasonable and correct answer.