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Photo (Properties) ( Details) GPS

Discussion in 'General Discussion' started by TomWolves, Apr 21, 2016.

  1. TomWolves

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    Hello fellow DJI flyers, How come when I look at my photo properties on my computer and go to details, then scroll down to GPS.The Altitude shows a wrong altitude I meanway off.
    It use to be in meters and I could figure out the imperial footage, now that I updated the app the altitude is way off and it could cause problems if someone needs these details for evidence on high they were flying.If I was only flying 200 feet and authorties checked my photo and it said I was flying over 400 feet, I'm going to be P O'ed (pissed off).In the photo you can see that I am not 285 feet or meters high.DJI just giving you heads-up or explain to me whats up, or how I can figure out my heighth.Thank you have a awesome day!
    Phant3ADV Properties Detail GPS.jpg
     
  2. msinger

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    What was the altitude in the DJI GO app at that time?
     
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  3. Shaba

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    Have you recalibrated? Similar thing happened to me when I switched to a new location for takeoff. After I recalibrated though, it was correct


    Sent from my iPhone using PhantomPilots mobile app
     
  4. TomWolves

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    msinger I was at 75 ft. this is according to the flight log. When I updated the Go app, that is when the reading in the properties GPS altitude was off. Before the update it was pretty accurate.
     
  5. GadgetGuy

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    No one at the FAA cares what altitude is being displayed in the app and recorded from there to the metadata of a still photograph. The DJI GO app does not and cannot measure AGL, which is the only relevant number to the FAA Guidelines. While I agree that the number displayed should be accurate relative to your launch point, your stated reasons for needing it to be accurate are unfounded. If the image was obviously taken at less than 400 feet Above Ground Level (AGL), your bigger concern, if it was shot commercially under a 333 Exemption, would be having permission of the property owner below to be there, and making sure your pilot's license is up to date! :cool: If it was a hobby shot, you are home free!
     
  6. Multicoptertec

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    True, the app itself doesn't "measure" anything, but reports altitude from the bird, which is AGL, no?
     
  7. TomWolves

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    I like to know how high the photo was taken, a friend of mine asked me,"how high was that picture taken of the condo?" I looked in the properties then details altitude. Well it certainly wasn't taken at 285 ft. it was 75 ft. I don't care about the FAA either!
     
  8. TomWolves

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    These are photo's taken from the SD card and put into my computer.
     
  9. GadgetGuy

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    Nope. That was my point. The bird cannot measure AGL. It only measures height relative to your launch point, which is irrelevant to the FAA. They only care about AGL, which you have to be aware of, and monitor independently! The world is not flat, although the DJI GO app pretends that it is. If the terrain around you ascends or descends, you must ascend or descend with it to stay at a fixed AGL. Otherwise, you will either run into the ground, or be well above 400 feet AGL, even though the app always shows a number above your launch point that is less than 400 feet. Hope that helps!
     
  10. Multicoptertec

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    Gotcha. I'm in Florida, where the world is actually flat.
     
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  11. GadgetGuy

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    Then you are golden! I live on a hill and fly to the bay and the ocean, so once I reach the water, I just subtract my home elevation to know how low, and negative, I can go without getting wet!:p

    Let us know if you get it sorted out. It's a useful metadata which is valuable for other reasons. I turn on the Subtitles .SRT sidecar file in DJI GO to add to my videos for the same reason, as it overlays the barometric elevation change as a subtitle on the video, when you enable it, during playback.
     
    #11 GadgetGuy, Apr 21, 2016
    Last edited: Apr 21, 2016
  12. Meta4

    Meta4 Moderator
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    The explanation for this is that a couple of firmware versions ago, DJI started putting the GPS altitude data in the field where they previously put barometer altitude.
    They still record barometer data in another field in the Exif data.
    The number you are seeing is what the GPS thought the altitude (ASL) was
    But GPS altitude accuracy is woeful and this can easily be +/- 200 feet or more.
     
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  13. GadgetGuy

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    Thanks for clarifying this. Do you happen to recall the name of the new field in the Exif data, to which the barometer data has been moved?
     
  14. Meta4

    Meta4 Moderator
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    No .. there's been a bit of discussion about this from photogrammetry users because it's screwed up their work.
    I'm back at Firmware v1.4 before the change so I can't tell.
    But Photoshop which shows full Exif data will show you.
     
  15. GadgetGuy

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    I can only imagine! I'm sure it's in LR as well. Just have to dig a little to find the right value.
     
  16. Meta4

    Meta4 Moderator
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    I can't imagine why DJI thought it was a good idea.
    They know how bad GPS altitude data is and that's why they don't use it for flying.
     
  17. GadgetGuy

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    Yes, they have definitely made some questionable decisions, along the way!
    Perhaps, they figured that GPS altitude data, that can be off by up to 200 feet is a truer value of ASL where the photo was taken from, than a somewhat meaningless value of elevation above or below a launch point, which could be over 3 miles away, with values that could only be 500 meters higher or 200 meters lower.
     
  18. Meta4

    Meta4 Moderator
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    GPS altitude data isn't just inaccurate.
    It swings all over the place too.
    At least the barometer doesn't vary much in the time your battery lasts but in that time GPS could be plus and minus 100 feet or more.
    It was a lot simpler to have all the images from a photo run in the same ballpark and be able to correct with ground control points rather than a bunch of different heights for photos taken from the same altitude.
     
  19. GadgetGuy

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    Certainly, from a photogrammetry standpoint, it's a nightmare! I used to run with a Garmin Forerunner and then upload the data to get a 3D view of the run. The software I was using had a correction algorithm to put your running route back on terra firma, instead of running below the surface or running in the air! GPS calculated altitude did vary wildly! My ski watch used a barometer, instead, to calculate total vertical feet skied for the day! Much more accurate. Off topic: My record was 67,000 vertical feet in one day! Places like Jackson Hole are great for setting vertical feet records. They even award pins and medals for vertical feet accomplishments, starting at 100,000 and 500,000 and 1,000,000.
     
    #19 GadgetGuy, Apr 21, 2016
    Last edited: Apr 21, 2016