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The Ground Sampling Distance (GSD) is the distance between the center of two consecutive pixels on the ground. It influences the accuracy and the quality of the final results as well as the details that are visible in the final orthomosaic.
The flight height H that is needed to obtain a given GSD can be computed and depends on the camera focal length, the camera sensor width [mm], and the image width [pixels].
Sw = real sensor width [mm] F_{R} = real focal length [mm] H = flight height [m] Dw = distance covered on the ground by one image in the width direction (footprint width) [m]

Some lens manufacturers give the focal length (F_{35}) in the 35 mm equivalent. It is not the 35 mm equivalent but the real focal length that should be used in Pix4Dmapper. In order to find the real focal length, some computations are needed. In the case of a 4:3 ratio, the formula for the real focal length F_{R} is given by:
F_{R} [mm] = (F_{35} * S_{W}) / 34.6 (1)
Where
F_{35 }= focal length that corresponds to the 35 mm equivalent
F_{R =} real focal length
Sw_{ }= the real sensor width
For more information about the 35mm equivalent focal length concept: Wikipedia article.
Using the fact that
H / F_{R} = D_{W} / S_{W},
the flight height H is given by:
H = (D_{W} * F_{R}) / S_{W} . (2)
The distance covered on the ground by one image in the width direction (footprint width) is given:
D_{W} = (imW * GSD) / 100. (3)
where
D_{W} = distance covered on the ground by one image [m] in the width direction (footprint width)
imW = image width [pixel]
GSD = desired GSD [cm/pixel]
Combining equation (2) and (3), the flight height is given by:
H [m] = (imW * GSD * F_{R}) / (S_{W} * 100) (4)
Index > Step 1. Before Starting a Project > 1. Designing the Images Acquisition Plan  Previous  Next 
What is the formula for the real focal length F(R) for a 3: 2 ratio?
Hi Lim,
In your case in the formula F_{R} [mm] = (F_{35} * S_{W}) / 34.6 you will have to substitute the f_{35} = 34.6 f /w mm with f_{35} = 36.0 f /w mm. The conversion you can find it here: https://en.wikipedia.org/wiki/35_mm_equivalent_focal_length .
Hence the formula will become F_{R} [mm] = (F_{35} * S_{W}) / 36 .0
Best,
Ina
thanks for Ina ^^
I have a sensor 1 / 2.3 CMOS and I can not find its width, it is the camera of a mavic pro Thank you
Hello Simón,
If you are talking about the width of the image, you can look its properties and you will fond it there.
Regards.
When planning a flight along a steep hillside, will the drone maintain a level flight path with respect to ellipsoid height or the geoid, or will it maintain its altitude with respect to the ground surface immediately below it?
Hi Carl,
there are some flight planning apps that follow the terrain instead of flying at a constant height. Typically, the flight plan is adjusted based on the specified digital surface/terrain model.
For example:
Best,