(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.