Decreasing the overlap can have an impact on the quality of the orthophoto due to vignetting in the
images. This effect can also occur when flying below a certain flight height for a specific lens size, or when
the texture of the area of interest is homogeneous (for example bare soil like a desert, short grass or low
growing crops).
Due to the image perspective, occlusions or hidden areas in vertical objects may occur, causing undesired
distortion effects. Delair recommends a minimum flight height of 120 m above vertical objects of interest,
such as buildings or bridges, in order to avoid distortion in the images.
During image acquisition, the UX5 HP has an average speed of 23.5 meters per second. Because of the
forward motion of the camera,
and depending on the flight height, the shutter speed should be set fast
enough to avoid blur effects on the imagery. Therefore, whenever ambient light conditions allow, Delair
recommends not to exceed half of the ground sample distance in forward motion during exposure.
Selecting the lens
The camera can be fitted with different sized lenses. The lens size you select depends on the tradeoff you
choose between resolution and area coverage:
l
A 15 mm lens offers wide coverage but lower resolution.
l
A 25 mm lens offers normal coverage and resolution.
l
A 35 mm lens offers lower coverage but high resolution.
Lens size
Resolution at 100 m (328 ft)
Diagonal view angle
15 mm
3.2 cm (1.3 ")
110.4 °
25 mm
2.0 cm (0.8 ")
81.6 °
35 mm
1.3 cm (0.5 ")
63.3 °
Note –
Take into account that the lens size can have an impact on the processed orthophoto due to
vignetting issues in the images. Delair strongly recommends correcting the images for vignetting when
using the NIR camera, or when using the RGB camera with a:
l
15 mm lens and flying below 100 m (328 ft)
l
25 mm lens and flying below 130 m (427 ft)
l
35 mm lens and flying below 260 m (853 ft)
21
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