fit.variogram {sgeostat} | R Documentation |
Fit variogram models (exponential, spherical, gaussian, linear) to empirical variogram estimates.
An object of class variogram.model represents a fitted variogram model generated by fitting a function to a variogram object. A
variogram.model object is composed of a list consisting of a vector of parameters, parameters
, and a semi-variogram model
function, model
.
fit.variogram(model="exponential", ...) fit.exponential(variogram.obj, c0, ce, ae, type='c', iterations=10, tolerance=1e-06, plot.it=F, weighted=T) fit.gaussian(variogram.obj, c0, cg, ag, type='c', iterations=10, tolerance=1e-06, plot.it=F, weighted=T) fit.spherical(variogram.obj, c0, cs, as, type='c', delta=0.1, iterations=10, tolerance=1e-06, plot.it=F, weighted=T) fit.wave(variogram.obj, c0, cw, aw, type='c', iterations=10, tolerance=1e-06, plot.it=F, weighted=T) fit.linear(variogram.obj, plot.it=F)
model |
only available for fit.variogram , switches what kind
of model should be fitted ("exponential", "wave", "gaussian",
"spherical", "linear" ). |
variogram.obj |
a variogram object generated by est.variogram() |
c0, ce, ae |
initial estimates for the exponential variogram model |
c0, cg, ag |
initial estimates for the gaussian variogram model |
c0, cs, as |
initial estimates for the sperical variogram model |
c0, cw, aw |
initial estimates for the periodical variogram model |
type |
one of 'c' (classic), 'r' (robust), 'm' (median). Indicates to which type of empirical variogram estimate the model is
to be fit. |
iterations |
the number of iterations of the fitting procedure to execute. |
tolerance |
the tolerance used to determine if model convergence has been achieved. |
delta |
initial stepsize (relative) for pseudo Newton approximation, applies only to fit.spherical |
plot.it |
if T, the variogram estimate will be plotted each iteration. |
weighted |
if T, the fit will be done using weighted least squares, where the weightes are given in Cressie (1991, p. 99) |
parameters |
vector of fitted model parameters |
model |
function implementing a valid variogram model |
fit.exponential
, fit.gaussian
and fit.wave
use an iterative, Gauss-Newton fitting algorithm to fit to an
exponential or gaussian variogram model to empirical variogram estimates.
fit.spherical
uses the same algorithm but with differential
quotients in place of first derivatives. When weighted
is
T
, the regression is weighted by n(h)/gamma(h)^2 where
the numerator is the number of pairs of points in a given lag.
http://www.gis.iastate.edu/SGeoStat/homepage.html
maas.vmod<-fit.gaussian(maas.v,c0=60000,cg=110000,ag=800,plot.it=T, iterations=30)