Figure 2.

(a) The definition of orientation for each pair of children, $r_{\mathit{ij}}$ is the distance between two children, and the orientation for a child i is defined by angle ${\theta }_i$, which is the angle between the direction being faced (red arrow) and the direct line between persons (blue line). A similar concept is applied to child j to obtain ${\theta }_j$. (b) The heatmap and (c) the 3D plot of $\beta (r_{\mathit{ij}},{\theta }_i,{\theta }_j)$ with $x=r_{\mathit{ij}}cos{\theta }_j$, $y=r_{\mathit{ij}}sin{\theta }_j$ and ${\theta }_i=0$ where child i is positioned at the origin and facing graph right. (d) The transition from infection to becoming infectious was 1 day; the incubation period (from infection to symptomaticity) had a mean of 4 days; the mean recovery time (from infection to infectious to recovered, i.e., non-infectious) had a mean of 10 days.