| est.variogram {sgeostat} | R Documentation |
Calculate empirical variogram estimates.
An object of class variogram contains empirical variogram estimates generated from a point object and a pair object. A
variogram object is stored as a data frame containing six columns: lags, bins, classic, robust, med, and n. The length of each
vector is equal to the number of lags in the pair object used to create the variogram object, say l. The lags vector contains the
lag numbers for each lag, beginning with one (1) and going to the number of lags (l). The bins vector contains the spatial midpoint
of each lag. The classic, robust, and med vectors contain the classical,
classic(h)= 1/n sum_(i,j)_in_N(h) (z(x_i)-z(x_j))^2
robust,
robust(h)=(1/n sum_(i,j)_in_N(h) sqrt(|z(x_i)-z(x_j)|) )^4/(0.457 + 0.494/n)
and median
med(h)=(med_(i,j)_in_N(h) sqrt(|z(x_i)-z(x_j)|) )^4/(0.457 + 0.494/n)
variogram estimates for each lag, respectively (see Cressie, 1993, p. 75).
The n vector contains the number |N(h)| of pairs of points in each lag N(h).
est.variogram(point.obj, pair.obj, a1, a2)
point.obj |
a point object generated by point() |
pair.obj |
a pair object generated by pair() |
a1 |
a variable to calculate semivariogram for |
a2 |
an optional variable name, if entered cross variograms will be created between a1 and a2 |
A variogram object:
lags |
vector of lag identifiers |
bins |
vector of midpoints of each lag |
classic |
vector of classic variogram estimates for each lag |
robust |
vector of robust variogram estimates for each lag |
med |
vector of median variogram estimates for each lag |
n |
vector of the number of pairs in each lag |
http://www.gis.iastate.edu/SGeoStat/homepage.html
maas.v<-est.variogram(maas.point,maas.pair,'zinc')