An instance of the point characterization algorithm. Points x (in red and black) correspond to the thinned lines of the extracted vessels. Green and blue points are the extreme points y computed by our DSaM algorithm. The yellow circle demonstrates the neighborhood of that point (). Red and black points lying in that circle are considered as neighbors of that extreme point. In that case, those points belong either to line cluster with index 1 or to line cluster with index 2. Thus,. The orange point corresponds to the nearest neighbor of y among the points of neighbor line cluster (black points). d is the minimum distance between the aforementioned nearest neighbor and the extreme points of its line cluster.