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Changing altitude

Discussion in 'General Discussion' started by Shaba, Feb 8, 2016.

  1. Shaba

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    I was flying this weekend in an open field with a small incline in elevation. In one area, there was a practice football field, and the particular field was approximately 5-7 feet higher than where I had launched my Phantom from. My question to the group relates to changing your landing area in respect to altitude. The football field was around 2000 ft from where I launched my Phantom, and again, around 5-7 feet from ground level than where I launched. I was just trying to practice flying some figure 8's, low level flights, and camera operations, when I noticed the height on my DJI app indicated on the football field that I was approximately 10 feet off of the ground. I could see from the camera though that I was looking from a horizontal position directly near the bottom of the football goal post, so I knew I wasn't 10 feet high. I went ahead and landed. After I took off again, the compass had recalibrated, and the new height was accurate while on the football field. At this point, I flew my Phantom back to my location, and sure enough, as soon as I began to descend, the height measurement was off again. I thought the sensors on the bottom of the aircraft were there to monitor that adjustment? I'm still learning, so please feel free to tell me I'm wrong, but with small of a difference in altitude in a semi-flat area, it makes me wonder how the same theory would pan out if I were in a mountain range, or area where there were multiple peaks/valleys?

    Any help and/or recommendations is greatly appreciated!

    Thank you!!
     
  2. yojo182

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    The sensors are only to keep the drone stable they are more or less cameras that scan the ground and hold it horizontally in place. The altitude is recorded on the internal barometer on take off and it can not adjust for changing terrain just altitude above sea level.


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  3. DroneDestination

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    Nope. The barometer records the INITIAL TAKEOFF HEIGHT as 0. So if I take off on a 300 foot hill, my altitude on the hill will be 0, but at sea level it will be -300ft.
     
    Buckaye likes this.
  4. yojo182

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    That's the point I was trying (not very well) to get across thanks for making it more clear.


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  5. DroneDestination

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    Lol no problem. Sometimes we just don't word things exactly the way we thought we did :D
     
  6. Mark The Droner

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    What the OP seems to be saying is the relative altitude changed when he flew to the football field and landed. The football field became the new relative altitude of zero, which made the relative altitude at the home point different.

    This is interesting. I've never heard of this, but then again, it's not often one flies a craft to a distant place, lands, then takes off.
     
  7. WetDog

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    I'm not sure that is what he meant ....

    I take it to mean that the OP was confused because 2000 feet away from his initial point, the P3 was showing him an obviously incorrect height over ground. He then landed the craft and 'recalibrated the compass'. I'm unsure exactly where he landed. If it was at the football field and he rezero'd the barometer (not the compass) then the goalpost height should make sense (although 10 feet seems a reasonable goalpost height???).

    I just take it that the OP is confused (as is typical) that the P3 does not calculate height over ground but instead calculates a height that is referenced to an arbitrary zero point (the starting point). It is a very important concept for a new flyer to understand and has caused no small amount of grief when understanding goes awry.

    It would be nice if the P3 had an x-band or LIDAR altimeter - I have an X-band Arduino module that I use to trigger a camera. It's only accurate to 100 feet or so, but I'd bet there are more powerful models. I'm willing to bet that DJI has or will work on incorporating such a technology. It would be more useful than the mediocre collision avoidance stuff that Intel is pushing.

    But for now, we're old fashioned and have to watch the map. Good initial question by the OP.
     
  8. Air Ontario

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    A US football goalpost crossbar height is actually 10 feet above the playing surface if I remember correctly.

    Also, I have landed my bird, brought the rotors to idle and after 10-20 seconds lifted off again and repeated that 3-4 times in a row but only within about 50-60 ft of myself. I have never tried it a 2000 ft away however. lol
     
  9. Mark The Droner

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    This makes perfect sense to me now. If the craft landed, the aircraft had to know it had landed. So the altimeter really has no choice but to reset and read a zero altitude at that point. Doing anything else would be silly, since it could now launch again if the pilot wanted. When it did launch, it used the new relative altitude.
     
  10. kennedye

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    That's really my only concern over the 500 meter hard limit; if I stand on a hilltop and fly 1700 feet below it (even while staying under 400 feet above the ground), I better not land or else I won't be able to reach my takeoff point again. Granted, it's not the worlds most common scenario.