Findclouds Manual 33
Example: Sun Object Ratio = 11950/11749 = 0.983
In the example the cloud coverage was only recognised by "Cloud Objects" and "Sun
Circle Ratio"
"Sun Circle Ratio":
Is another characteristic value to determine state of sun. It deals with the
special problem to determine between sun on clear sky and sun behind continuous cloud coverage
producing a spot.
( <level → SunOnClearSky )
A sun on clear sky causes rays by the optic and the sun object will appear jagged. A sun shining
through clouds is smoothed and appears circular.
The "Sun Circle Ratio" tells, how good the sunpixel match to a circle. In the images on the right
hand side it is obvious, that the sun is much more "circle like" than the jagged clear sky sun.
Ratio Brightpix/Sunpix:
Tells about haze or thin clouds in front of the sun. On clear sky the ratio
is less than 2 and rises with amount of haze or thin clouds.
( <2 → SunOnClearSky )
Brief overview of level inputs:
"Level Sun Pixel":
If the value of the pixel of the intensity image is higher than this level, it is
classified as sun pixel. For badly underexposed images it might be necessary to reduce this value.
"Min. Object Size":
''Sun Objects'' & ''Cloud Objects'' that contain less number of pixel will be
discarded.
"Level Sun Object Ratio":
If ''Sun Object Ratio'' is > Level → SunOnClearSky.
"Level Sun Circle Ratio":
If ''Sun Circle Ratio'' is < Level → SunOnClearSky.
"Level Ratio Brightpix/Sunpix":
If "Ratio Brightpix / Sunpix" is > Level → SunBehindClouds (&
value exists).
