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Obtaining true drone camera parameters to calculate ground sampling distance

Samot484

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Apologies if this is a stupid question, but I’m quite new to cameras/drone cameras! Does anyone know how you extract the true sensor diameters and focal length of a drone’s camera from the specs listed on the DJI website as I understand these are standardised? I’m trying to calculate Ground Sampling Distance for the Mavic 2 Pro and the Mavic 2 Enterprise Advanced at different altitudes and the values I’m getting are a lot smaller than I expected and so I think I must have the wrong values for sensor width and focal length (or gone wrong somewhere else). Thanks very much for any help in advance! Below are the values I’m currently using…


GSD = (sensor width (mm) x altitude (m) x 100)/(focal length (mm) x image width (pixels))

Mavic 2 Pro:

Sensor width = 13.2mm, focal length = 28mm, image width = 5472 pixels

GSD at 40m = 0.3446 cm/pixel

Mavic 2 Enterprise Advanced:

Sensor width = 6.4mm, focal length = 24mm, image width = 8000 pixels

GSD at 40m = 0.1333cm/pixel



Values sourced from DJI website (see links below) and then I’ve attempted to adjust them to true values based on some reading I did online but I’d imagine I may well have got this wrong.

M2P: Mavic 2 - Product Information - DJI

M2EA: Mavic 2 Enterprise Advanced - Specs - DJI



Thanks very much again!
 
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Values sourced from DJI website (see links below) and then I’ve attempted to adjust them to true values based on some reading I did online but I’d imagine I may well have got this wrong.
Your focal lengths are completely wrong.
You have used the 35mm equivalent which isn't the actual focal length of the lens which is much smaller.
You could find the focal length by looking at the image metadata.
 
Great, thanks very much for your replies, I've found the correct values in the image metadata now. Do you know if those values for sensor width sound about right?
 
Yes. If you are using a Windows PC, you can look at the properties (Properties>Details) of an image and see the actual pixel Width and Height.
I'm sure you can do the same on an IOS machine, but I am not familiar with those.
 
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