Automated Individual Tree Isolation on High-Resolution Imagery: Possible Methods for Breaking Isolations Involving Multiple Trees

One of the key problems in automated individual tree crown delineation, whether from multispectral or lidar data, is the grouping of several trees into a single tree crown outline (isol). Using airborne multispectral imagery, we explored four approaches to breaking such isols into multiple crowns: “core,” “tree top,” “template matching,” and “basin” breaks. Core breaks are made using only isol shape and morphological primitives. Tree top and template matching breaks utilize image maxima and pattern, and watershed drainage basins form the basis of basin breaks. The effectiveness of each of the four break types was assessed against the presence and position of the true boundary between multiple tree crowns and with reference to original isol shape. There was correspondence and differences between breaks of different types. A set of rules was developed to choose a single break when there was positional correspondence of several break types. The rules were based on isol shape type and the break types present. Despite being a complex and difficult issue, it was shown that the concept of identifying poor delineations, recognizing them as cases of multiple trees, and remediating the crown delineations is viable and worthy of further development.