Using ray-traced templates to find individual trees in aerial photographs

To estimate positions of individual trees in high–resolution aerial photographs we use circular templates derived from an optical tree crown model and the geometry at image acquisition. A straight–forward analysis method consists of finding local maxima of the correlation function for the successively transposed templates over the whole image. Three ways of improving this method are discussed. Performance is evaluated by use of data from a thinning experiment in Norway spruce. It turns out that images where the trees are backlighted by the sun are particularly well suited for our approach.