(f(rj)
f(rj+h)) separated by distance h.
This empirical function is fitted into a particular semi-variogram model; there are a number of models. Sironvalle (1980) has discussed about quadratic model. Kitanidis (1997) has discussed about linear model and is most widely used model. Cressie (1991) discussed about an exponential, rational quadratic and wave model. Paninatier (1996) has discussed about Gaussian, power and spherical models. Olea (2000) has discussed about pent spherical and cubic model. The function is fitted for the input points within the search radius and then the value is predicted at a specified point. Unlike IDW, the predicted values can exceed the numerical value of sample points.