Fig. 3

Wing/body characterization and spectral clustering. A–D Fly position and heading definition. A A schematic of a fly. B Torso ellipse fitting; the centroid of the torso (blue cross) denotes the position of the fly. The two ends of the major axis (green points) were assigned as the candidates for the head and tail. C The centroid of the whole body (red cross). D A candidate further to the centroid of the whole body is designated the head (blue point), and the other candidate is assigned to the tail (red point). The heading is the vector pointed from the centroid of the torso to the head point. E–G Wing extension angle calculation. E Edge of the wing calculation (red edge). F The wing is separated into right and left sides by a cross-product. The wing tips are defined as the farthest edge points from the centroid of the torso (the green and yellow points). G The wing extension angles (θ and θ’) between the wing tips and the major axis of the torso can thus be calculated. H The process of spectral clustering