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James Mitchell
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Flight distance : 41673 ft

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Hello,

I would like to be able to  work out how much area is covered by an image when taken straight down from different heights.

For example, 10m altitude = 2x2m. 20m altitude = 5x5m etc

Does anyone know the answwers or how to work it out? I have takne the photos.

Thank you for any help

James
2018-6-12
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DJI Natalia
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Hello. May I know which DJI aircraft you are referring to? Thank you.
2018-6-12
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James Mitchell
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Flight distance : 41673 ft

United Kingdom
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Hello, yes it is a DJI Phanton 4 Pro.
2018-6-12
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Eric13
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James Mitchell Posted at 2018-6-12 07:28
Hello, yes it is a DJI Phanton 4 Pro.

You can calculate it. See the following link and scroll down to "Part 5":
https://learn.droneblocks.io/courses/droneblocks-math-with-drones/lectures/2908697
2018-6-12
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DJI Diana
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James Mitchell Posted at 2018-6-12 07:28
Hello, yes it is a DJI Phanton 4 Pro.

Hi James, you can check the specs of the Phantom 4 pro from the website: https://www.dji.com/phantom-4-pro/info#specs, please calculate it according to the specs of the drone. Thanks.
2018-6-12
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DJI Diana
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Eric13 Posted at 2018-6-12 11:19
You can calculate it. See the following link and scroll down to "Part 5":
https://learn.droneblocks.io/courses/droneblocks-math-with-drones/lectures/2908697

Nice information. Thanks for your sharing.
2018-6-12
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James Mitchell
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Flight distance : 41673 ft

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Thank you so much for this. Very helpful.

Just a couple of questions. I assume the height in the image file is height above sea level and not the height above ground level? It does not seem correct.

In cannot find the sensor width for the Phantom 4 Pro. Is is 13.2mm?

Thank you for any further help.
2018-6-13
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Antonio76
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James Mitchell Posted at 2018-6-13 00:24
Thank you so much for this. Very helpful.

Just a couple of questions. I assume the height in the image file is height above sea level and not the height above ground level? It does not seem correct.

Question 1) the height is above ground, not ASL. It is from the takeoff location. EDIT Sorrry, of course this is wrong. The exif data from the picture report the GPS height, which is from Sea leve (but it is not precise at all...)
Question 2)  I would take a different approach. what matters is the field of vue (FOV) of the camera, not the size of the sensor.From the height of the camera and the FOV you can calculate the diagonal of the recorded image in meters, and from there the area. You will also need to know the aspect ratio of the image, from the camera settings.  These images will help you...EDIT: Sorry, the pictures should be in reverse order. first one to be looked at after the second one... ALSO: in the second picture it should read "Consider the triangle AVB" , NOT AVC.

area of picture - 2.jpg
area of picture-1.jpg
2018-6-13
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Eric13
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James Mitchell Posted at 2018-6-13 00:24
Thank you so much for this. Very helpful.

Just a couple of questions. I assume the height in the image file is height above sea level and not the height above ground level? It does not seem correct.

Yes - it seems to be 13.2mm.
When you do the calculating - make sure your image ratio setting is not 16:9.
https://www.dxomark.com/Cameras/DJI/Phantom4-Pro---Specifications
2018-6-13
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James Mitchell
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Flight distance : 41673 ft

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Thank you everybody for your comments. I really appreciate it.

The details from the jpg shows an altitude of 186.491 but i took the image at 120 metres. That is why i am wondering if it is the height above sea level.

Thank you
2018-6-13
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Antonio76
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James Mitchell Posted at 2018-6-13 03:04
Thank you everybody for your comments. I really appreciate it.

The details from the jpg shows an altitude of 186.491 but i took the image at 120 metres. That is why i am wondering if it is the height above sea level.

Don't count on the Exif data for a correct altitude... and of course you should also consider if the altitude of the ground under the drone is the same as the takeoff point... You can check that in googleearth, for example.
2018-6-13
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Eric13
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James Mitchell Posted at 2018-6-13 03:04
Thank you everybody for your comments. I really appreciate it.

The details from the jpg shows an altitude of 186.491 but i took the image at 120 metres. That is why i am wondering if it is the height above sea level.

In the following thread that issue is being discussed. I understand that GPS is bad for height calculation.
But I'm wondering why the Barometer is not used for that:
https://forum.dji.com/thread-152389-1-1.html
2018-6-13
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KedDK
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Eric13 Posted at 2018-6-13 03:27
In the following thread that issue is being discussed. I understand that GPS is bad for height calculation.
But I'm wondering why the Barometer is not used for that:
https://forum.dji.com/thread-152389-1-1.html

Yes in this one too ...
2018-6-13
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