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Drone height for object that is x wide
1039 13 2017-8-6
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chrismid2599
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Hello.

I'm planning on photographing a lake that is 50 metres wide. I want to photograph this lake top-down with a drone. How do I figure out what height I would need to be to be able to fit the lake into the frame? I'm no master as Maths, and I have Googled a few terms to see if anyone else has asked this question but haven't found anything.

Any help would be appreciated.
2017-8-6
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G Davidson
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Ball park figure would be approx 30m if using a Phantom 4 standard
2017-8-6
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Rodger8
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The best way to do this is with a mapping program. I usually do all of my maps at 155 feet AGL that way I have a high resolution image to work with. Be sure to  extend your boundaries to allow for cropping of the final image.
2017-8-6
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Mike Mas
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Forget all the math, just fly over the lake point down and climb until it's in frame.

Regards
2017-8-6
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Irate Retro
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Where FOV is the field of view for your camera in degrees, the formula would be:
required_height =  object_width / (2*tan(FOV/2))

For a 94 degree FOV on the P4 std, and a 50 meter lake, the answer would be 23.31 meters.
2017-8-6
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G Davidson
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Irate Retro Posted at 2017-8-6 12:24
Where FOV is the field of view for your camera in degrees, the formula would be:
required_height =  object_width / (2*tan(FOV/2))

Nearly there...  I believe the 94 degree field of view is diagonal. I think the horizontal FOV is about 82 degrees making the height nearer 29m so throwing in a few more meters in height would allow for minor errors in keeping the camera framed centrally.
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Irate Retro
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G Davidson Posted at 2017-8-6 12:46
Nearly there...  I believe the 94 degree field of view is diagonal. I think the horizontal FOV is about 82 degrees making the height nearer 29m so throwing in a few more meters in height would allow for minor errors in keeping the camera framed centrally.

Thanks.  I did not know that the claimed FOV was (possibly) diagonal.  It seems logical though.

Mike Mas- You can't always just forget the math and fly up to see it on the screen.  Particularly if you're storing waypoints and setting the aircraft off on an autonomous mission, while you are sitting at home miles away (out of RC range) in the cool air conditioning sipping a scotch.
2017-8-6
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Labroides
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My calculations indicate that if you are flying a P4 pro at 50 metres, the camera would cover an area of about 50m x 75m.
2017-8-6
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Kneepuck
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Irate Retro Posted at 2017-8-6 13:42
Thanks.  I did not know that the claimed FOV was (possibly) diagonal.  It seems logical though.

Mike Mas- You can't always just forget the math and fly up to see it on the screen.  Particularly if you're storing waypoints and setting the aircraft off on an autonomous mission, while you are sitting at home miles away (out of RC range) in the cool air conditioning sipping a scotch.

I'm trying to figure out if that's  hedonistic, decadent or both.
2017-8-6
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G Davidson
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Irate Retro Posted at 2017-8-6 13:42
Thanks.  I did not know that the claimed FOV was (possibly) diagonal.  It seems logical though.

Mike Mas- You can't always just forget the math and fly up to see it on the screen.  Particularly if you're storing waypoints and setting the aircraft off on an autonomous mission, while you are sitting at home miles away (out of RC range) in the cool air conditioning sipping a scotch.

The P4 spec sheet I looked at did not mention that the FOV figure was diagonal but it seems many have had the same question and the general consensus is that the diagonal FOV is 94 degrees. Just to add to the confusion, the diagonal FOV will change with the aspect ratio and thus possibly different between movie and still shots! At least the horizontal FOV should remain the same in either aspect ratio.

As you rightly say, the quickest way is just to watch the picture and climb to get the desired view
2017-8-6
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G Davidson
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Labroides Posted at 2017-8-6 14:17
My calculations indicate that if you are flying a P4 pro at 50 metres, the camera would cover an area of about 50m x 75m.

You've reminded me of some concerns I had about the P4 Pro  after I saw RAW geometrically uncorrected images from one shortly after release - some fairly moderate lens distortion was being corrected by its lens profile resulting in quite a crop of the image extremities. The image pixel count  still appeared to match the sensor pixel count  after the crop which left me wondering if even after having a 20mpix sensor we truly got a practical resolution boost over the 12Mpix P4 given the cropping, distortion correction and apparent rescaling back to 20 Mpix.  In mitigation, there was also that longer focal length to factor in too. If only I could borrow a P4 pro to do a practical comparison with my P4! (Aerial 360). Having said that, who knows what improvements may be present in DJIs next offering with Hassleblad perhaps in the loop!

Anyway, I don't want to be rude and drag the thread off topic!
2017-8-6
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Labroides
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Lens viewing angles for all cameras are always the diagonal angle.
2017-8-6
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chrismid2599
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Thanks for all your comments. I’m using a P4Pro. I believe the FOV of 84 degrees. I’m shooting stills in 16:9 ratio.
2017-8-7
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Labroides
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chrismid2599 Posted at 2017-8-7 11:29
Thanks for all your comments. I’m using a P4Pro. I believe the FOV of 84 degrees. I’m shooting stills in 16:9 ratio.

Why shoot 16:9?
If you want the maximum area, use 3:2.
2017-8-7
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