How Does Litchi Control Altitude?

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Last fall I reported that a Litchi mission that had been operating very well, flying over tree tops, crashed into the branches of a tree with no leaves. The consensus from knowledgeable forum guys was that the drone "didn't see" the branches as they were now leafless. and crashed into them. I flew the mission again this week, still no leaves on the trees here in Pennsylvania. I was planning to pause (stop) the mission when it got close to the "problem" tree. As I watched closely, the drone cleared the tree easily seeming to never change altitude.

So my question: How does Litchi control altitude? Could the crash last fall have been caused by an air pressure problem? An ion storm. :)

Seriously, any insights are appreciated.
 
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Last fall I reported that a Litchi mission that had been operating very well, flying over tree tops, crashed into the branches of a tree with no leaves. The consensus from knowledgeable forum guys was that the drone "didn't see" the branches as they were now leafless. and crashed into them. I flew the mission again this week, still no leaves on the trees here in Pennsylvania. I was planning to pause (stop) the mission when it got close to the "problem" tree. As I watched closely, the drone cleared the tree easily seeming to never change altitude.

So my question: How does Litchi control altitude? Could the crash last fall have been caused by an air pressure problem? An ion storm. :)

Seriously, any insights are appreciated.
I believe the Phantoms use an altimeter and barometric pressure to determine altitude. Environmental factors can affect accuracy. Litchi merely follows instructions and uses that data throughout the flight.
 
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Launching at slightly different locations can also affect the altitude reading. If the software registers the barometric pressure as zero altitude when launching from ground level, there will probably be 3 ft of difference if launching the next time from a picnic table in the same area.
 

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So my question: How does Litchi control altitude? Could the crash last fall have been caused by an air pressure problem? An ion storm. :)
How close to the tree have you been flying with this mission?
Is it a vertical clearance issue that clipped the tree or perhaps horizontal positioning?
Both GPS for horizontal and barometric sensor for vertical positioning are only approximate and you really need to allow a safety margin of at least 20 ft from obstacles when programming a waypoint mission.
 
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Litchi uses the barometric pressure at the takeoff point as the reference point for all further altitude calculations. It then uses map data to calculate offsets from that point based on the waypoint locations plotted on the map to control the flight. These offsets all shift up or down if you take off from a point different from the original launch point.

An additional problem comes from the fact that the DJI pressure sensor is not very accurate. It can read different heights measured in feet, or 10s of feet in exactly the same situation. At low altitudes the optical sensors looking down can make corrections, but above their working distance the drone relies only on the instantaneous air pressure.
 

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