Fig. 5 (e) illustrates the first-order neighboring polygons (indicated by red lines) and second-order neighboring polygons (indicated by green lines) for building polygon A. As observed in Fig. 5 (d), within the Voronoi tessellation model, unlike regular images (of a single pixel are 8), the number of neighboring units for an individual building polygon may be greater or less than 8, and their directions are not restricted to fixed 8 directions (0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°). Instead, they are distributed in the range θ ∈ [0°, 360°). Therefore, when constructing the texton co-occurrence matrix for a cluster of building polygons, it is necessary to partition the directions to determine the principal directions. This aspect will be elaborated upon in detail in Section 2.2.3.