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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 quality of the final results and the details 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].
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Sw = real sensor width [mm] FR = 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 (F35) in the 35 mm equivalent. It is not the 35 mm equivalent but the real focal length that should be used in PIX4Dmapper. 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 FR is given by:
FR [mm] = (F35 * SW) / 34.6 (1)
Where
F35 = focal length that corresponds to the 35 mm equivalent
FR = 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 / FR = DW / SW,
the flight height H is given by:
H = (DW * FR) / SW . (2)
The distance covered on the ground by one image in the width direction (footprint width) is given:
DW = (imW * GSD) / 100. (3)
where
DW = 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 * FR) / (SW * 100) (4)
H = (imW * GSD* FR ) / (Sw * 100) = (4000 * 5 * 5) / (6.17 * 100) = 162.07 [m]
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What is the formula for the real focal length F(R) for a 3: 2 ratio?Hi Lim,
In your case in the formula FR [mm] = (F35 * SW) / 34.6 you will have to substitute the f35 = 34.6 f /w mm with f35 = 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 FR [mm] = (F35 * SW) / 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,
Bonsoir ,j'aimerai savoir comment paramétrer les options de traitement des trois étapes dans PIX4DMAPPER afin d'avoir un très bon fond topo ?
Hello Bangaly,
There is training for it so please feel free to contact us if you are interested in it. In general, it is not easy to recommend a particular setting for a topographic map as it also depends on the images uploaded. If you are not sure what to select, I suggest using the default setting first after selecting the templates you want (click here for more information), then, open the quality report and change the setting according to the result. The website, Quality Report Help, would be helpful to decide what to change as it explains the setting based on the result of the quality report.
Regards,