Findclouds Manual 38
The following example shows some "forward projections" containing gaps to demonstrate effect of
rising angles and loss of image content.
To make the images more demonstrative not a sky image was used, but an image of laboratory
window.
First image is original fisheye lens image, second is projection of 60°, third of 80° and forth of 85°.
These images demonstrate how the image content evolves with zenith angle.
For 60° projection there are only small gaps that need to be filled. For 80° it is clear to see that
from half the image radius on, large areas must be interpolated from small pixel informations. For
85° angle the image content is restricted to a small region in the middle and most of the image
must be interpolated.
In praxis the zenith angle should be restricted to values <80°. For opacity classification (CDOC
algorithm) the scientists recommended not to exceed 70° of zenith angle (Field Of View < 140°).