Figure 4

Schematic overview of the pseudo skeleton calculation. The figure illustrates the general procedure used to derive a pseudo-skeleton, therefore all vertices, contours, etc. are schematic drawings and not based on data or results of the algorithms. The pose detection uses the center of the ellipse detected by LACE_HTD toolbox as the center for a simple contour detection (solid orange line) via Canny's edge detector. One hundred evenly spaced pixel-coordinates (translucent orange dots) on the contour are chosen. Note that these contour-coordinates are not evenly spaced in the schematic drawing. These contour-coordinates are used as seeding coordinates for Voronoi cells (teal colored lines and dots). A Voronoi cell encompasses all space that is closer to its contour coordinate than to the other contour coordinates. Each cells is enclosed by a number of edges. The Voronoi calculation also generates edges of the Voronoi cells outside the contour of the animal, which are ignored in the algorithm and therefore not drawn here. These Voronoi-edges (teal lines) are represented by their vertices (teal dots). The algorithm selects the vertices that are inside the animal's contour for further computation. Those central Voronoi-edge vertices are now used in Dijkstra's path algorithm to select (teal dots with orange border) the central line along the anteroposterior-axis (dashed orange line).