AI-GEOSTATS: Random Functions

[Digby Millikan]

Hello,    I am reading some geostatisitics texts, and they introduce random functions. Some texts say;         A deposit D is made of a set of random variables Z(x) which make up a random function.                  Z(x) is hence a set of possible realizations e.g. z(x)    I understand this, however in Geostatisitics: Modeling Spatial Uncertainty and                                            Geostatisitics for Engineers and Earth Scientists    The term w is introduced representing the sample space(?)       i.e.   a random variable is Z(x,w)    This I do not understand. If w is part of the sample space e.g. a range of possible grades at a point then this is saying the grade Z(xi,wi) is a function of itself w. Is this how this term is supposed to interpreted? What is w?