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height vs video width

Discussion in 'Pro/Adv Discussion' started by phantomadv_2000, Jul 7, 2015.

  1. phantomadv_2000

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    Dear Pilots

    I'm planning a flight where i'll be filming straight down, i'm hoping to be able to fit an area 400 meters wide into the frame, the question is: is there a way to anticipate the required flying height?

    Best regards
     
  2. ctp

    ctp

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    The camera has a 94 degree FOV. If I understand that math correctly, and we simplify and call it a 90 degree FOV it becomes a simple right angle. Bisect the triangle for simple math and you have 2 triangles 200m wide at the base (400m ground coverage). Because it's a right angle, the height will equal the base (200m) of each triangle.

    Put it all together and a height of 200m should get you ground coverage of 400m on the wide side with the camera pointing straight down. A 16:9 picture (video?) is 4000x2250, so in theory your picture will cover 400m by 225m.
     
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  3. bobmyers

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    Say What! :confused:
     
  4. ctp

    ctp

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    A video taken at 200m height should frame an area roughly 400m by 225m with the camera pointed straight down. If my math is correct :)
     
  5. Elfman12

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    I was told there would be no math required. ;)
    (nice cypherin')
     
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  6. bobmyers

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    I will take your word on ito_Oo_Oo_O
     
  7. Meta4

    Meta4 Moderator
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    The maths is a bit much for me to get my head around at this hour but the FOV of the lens is calculated diagonally rather than horizontally.
    Does this change the calculations?
     
  8. taroh

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    90 deg is good approximation. Instead 400m of diagonal, the width be 400m then diagonal 500m, then heght 250m. And FOV is based on 4:3 imager, not 16:9. I also made same mistake and pointed out on another math thread here. :)
     
  9. loganboyd

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    You just need to use a FOV calculator and know the 35mm focal length equivalent of the lens.
    You can see from the first part that the focal length of around 20mm gives us roughly 94 degrees FOV diagonally. I'm not sure if that's what the 94 for the phantom means or if it is a horizontal FOV. If it is, then adjust the focal length lower until you get 94 horizontal degrees.
    In the 2nd part, punch in the same focal length and adjust the distance to subject until your horizontal distance gets to be 400m.
    Calculators can be found here: http://www.tawbaware.com/maxlyons/calc.htm

    FOV Calculator.PNG
     
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  10. loganboyd

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    Keep in mind that the height shown in the Pilot App uses the ground level from where you take off. If the area you are photographing is some place that you have to fly to then that ground elevation may be +/- so the height in the Pilot App won't be accurate.
    This is why we need frickin' laser beams on our drones so we can get a super accurate height reading :)
     
  11. wordsmith

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    Yeah. And they'll come in handy when we use our P3's for world domination.
     
  12. phantomadv_2000

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    Thanks a lot for all the replies:)
     
  13. paulajayne

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    Fly at 10,000 metres you will get it all in then. :rolleyes:
     
  14. sergekouper

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    Sure that helps to have a brain in working order... :)
     
  15. YolevonALLin

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    I did a 'test' shot with my old P2 to test something similar.. it was one of our 2.5 - 3mm sq foot plants, so close in size to you. Wind was brutal that day at about 35 mph on the gorund and who knows what from the air, but I was up at about 450ft for this picture. I plan to get a fuller one here in the next few weeks from more above/higher.
     

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  16. loganboyd

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    This was a very good approach except the 94 degree FOV is diagonal and not horizontal. This puts the needed height about 10-15% higher than your estimate from this.
     
  17. Chuck Young

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    So I just did a little testing and 10 feet away from the camera lens the field of view for video at 4K of 19 feet, at 1080 it is 16.5 feet, Still shots at 16X9 are 17 feet, 4X3 is 16.5 feet.

    So depending on how much of the sensor is being read, the field of view is different. This was by no means scientific. To be exact you would need to know the sensor dimensions and the pixel size and the number of pixels being read at each resolution and the focal length of the lens. Just saying.