Fig. 3

The Euclidean distance transform contour tree. The Euclidean distance transform (left) shows the distance from each point in the void space to the nearest point of biomass (black). Critical values are shown as labeled points A–E on the EDT figure. At right is the EDT contour tree. Note that critical points in the EDT correspond to leaves and branch points in the contour tree, and that the vertical position of nodes in the contour tree correspond to EDT values of those critical points (also depicted with colors on the contour tree). The dashed curve on the EDT corresponds to a particular level set of the EDT, and clearly contains two connected components. Due to the vertical ordering of the tree, those components are also visible as the intersection points of the dashed isoline with the contour tree