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RTH Altitude Considerations with Varying Terrain

Discussion in 'General Discussion' started by SoCalDude, Oct 4, 2016.

  1. SoCalDude

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    Is there a thread or web page that explains the various considerations when setting the Return To Home altitude? What I mean is how to account for various scenarios with varying levels of terrain?

    For example, if I take-off up on a bluff/cliff (my home point), which as 30' trees. Normally, I would set the RTH altitude to maybe 40-50'. Now, I fly over an area (the valley) that has a lower ground level than the home point. Let's say it is 75 feet lower. Do I need to consider this 75' in my RTH altitude? In this scenario, should my RTH altitude be 125'. Does it matter that I'm flying above this lower valley at 200' above the home point (which is 275' above the valley floor)?

    This raises another question, is the current flying altitude shown in the Go app relative to the home point or the valley floor below?

    Thanks for any insight to help this newbie!
     
  2. msinger

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    It's relative to the take off point -- as is the RTH altitude.

    You should set the RTH altitude to at least 50 feet higher than the tallest known obstacle above the takeoff location. 10 feet is not enough buffer since the altitude can be easily off by 20 feet once your Phantom is up in the air. The RTH altitude can only be set in meters, so keep in mind you'll need to translate feet to meters as you're changing that setting in DJI GO.

    No -- since the RTH altitude is relative to the take off location. If you take off, ascend 20 feet, and fly over a cliff, your current altitude will still be 20 feet in DJI GO.
     
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  3. Meta4

    Meta4 Moderator
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    The only altitude your Phantom knows or understands is Home = zero.
    Everything else is relative to that.
    Just make sure your RTH height is high enough above your home point to clear any obstacles that could be between the Phantom and home.to clear
     
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  4. SoCalDude

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    50' buffer (15 meters)...that's good to know. :)

    Thank you, @msinger.
     
  5. ResOps

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    not to beat this topic to death but I don't think my question is fully answered.

    my home point take-off is 950'asl. But i am surrounded by 1320;asl hills on 3 sides so when i go over the hill into the next valley ,which is again at 950'asl and hit RTH, which is at 50m (165'asl) am I dead or does the drones gps keep me 165' above it's current geographical location. If I read right it is 165' as seen from home-point.
     
  6. SoCalDude

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    You'll need to set your RTH height to 1320 feet minus 950 feet, which equals 370 feet. The height of the other valley floors is irrelevant.

    Two notes on this scenario...
    1. This calculation does not take into consideration the height of any trees or other vertical obstructions on the top of said hills.
    2. The aforementioned 370 feet calculation result needs to be converted to meters and entered into the DJI RTH Height setting. (it only accepts values expressed in meters)
     
  7. msinger

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    The RTH altitude is the height above the takeoff point (which is always 0 meters). The Phantom's altitude is calculated using its internal barometer, so you should add at least 15 meters to whatever you think the RTH altitude should be to add a buffer for any error in that calculation (it's usually not 100% accurate).