with
\(I_{r}(u_{\text{ij}})=\left\{\par \begin{matrix}\ \ 1,\ \ \ \ \ \ \ \ \ u_{\text{ij}}<r\\ 0,\ \ \ \ \ \ \ \ \ \ \ u_{\text{ij}}>r\\ \end{matrix}\right.\ \) and 0≦\(I_{r}(u_{\text{ij}})\)≦1 (1)
Where N is the total number of trees, and \(u_{\text{ij}}\) is the distance between i and j.
The K-function can be normalized as L-function proposed by Besag (1977):