@book {Hengl2003KED,
	title = {{Comparison of kriging with external drift and regression-kriging. Technical report}},
	year = {2003},
	pages = {18},
	publisher = {International Institute for Geo-information Science and Earth Observation (ITC)},
	organization = {International Institute for Geo-information Science and Earth Observation (ITC)},
	address = {Enschede},
	author = {Hengl, T. and Heuvelink, G.~B.~M. and Stein, A.}
}