Schlather, M., A. Malinowski, P. J. Menck, M. Oesting, and K. Strokorb. “Analysis, Simulation and Prediction of Multivariate Random Fields With Package RandomFields”. Journal of Statistical Software, vol. 63, no. 8, Feb. 2015, pp. 1-25, doi:10.18637/jss.v063.i08.