We are estimating canopy cover/leaf area index for forests where we have been Malaise trap sampling using Gap Light Analyzer 2.0 software but do not know the projection distortion (polar, Lambert's equal area, orthographic or stereographic equal area) of the lens we have used. We took our photos with a Sigma EX DG fisheye 8mm 1:3.5 lens. Does anyone know the projection distortion of this lens?
I've no information about a matrix you can use to correct your pictures, but photographic softwares such as DxO or Adobe Lightroom can do it directly. For instance, using Lightroom 4 or 5, you can select lens correction and choose the good lens. It will correct lens weaknesses including distortion. You can have a look at screenshot attached (Lightroom 4, but french version, sorry).
I was not aware that those packages could be used for canopy cover/leaf area index estimation so I will trial them. Promising that our lens is among the available selections. Merci
You can find some information in the following publication:
Lang, M., Kuusk, A., Mõttus, M., Rautiainen, M., Nilson, T., 2010. Canopy gap fraction estimation from digital hemispherical images using sky radiance models and a linear conversion method. Agricultural and Forest Meteorology 150, 20–29. doi:10.1016/j.agrformet.2009.08.001
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