autofitVariogram {automap} | R Documentation |
Automatically fitting a variogram to the data on which it is applied. The automatic fitting
is done through fit.variogram. In fit.variogram the user had to supply an initial estimate for the sill,
range etc. autofitVariogram
provides this estimate based on the data and then calls fit.variogram.
autofitVariogram(formula, input_data, model = c("Sph", "Exp", "Gau", "Ste"), kappa = c(0.05, seq(0.2, 2, 0.1), 5, 10), fix.values = c(NA,NA,NA), verbose = FALSE, GLS.model = NA)
formula |
formula that defines the dependent variable as a linear model of independent variables; suppose the dependent variable has name 'z', for ordinary and simple kriging use the formula 'z~1'; for simple kriging also define 'beta' (see below); for universal kriging, suppose 'z' is linearly dependent on 'x' and 'y', use the formula 'z~x+y'. |
input_data |
An object of SpatialPointsDataFrame-class. |
model |
The list of variogrammodels that will be tested. |
kappa |
Smoothing parameter of the Matern model. Provide a list if you want to check more than one value. |
fix.values |
Can be used to fix a variogram parameter to a certain value. It consists of a list with a length of three. The items describe the fixed value for the nugget, range and sill respectively. Setting the value to NA means that the value is not fixed. |
verbose |
logical, if TRUE the function will give extra feedback on the fitting process |
GLS.model |
If a variogram model is passed on through this parameter a Generalized Least Squares sample variogram is calculated. |
Geostatistical routines are used from package gstat
.
A few simple choices are made when estimating the inital guess for fit.variogram
.
The initial sill is estimated as the mean
of the max
and the median
of the semi-variance. The inital range is defined as 0.10 times the diagonal of the bounding
box of the data. The initial nugget is defined as the min
of the the semi-variance.
There are five different types of models that are often used:
A list of all permitted variogram models is available by typing vgm() into the R console.
autofitVariogram
iterates over the variogram models listed in model
and picks the model
that has the smallest residual sum of squares with the sample variogram. For the Matern model, all the
kappa values in kappa
are tested.
An object of type autofitVariogram
is returned. This object contains the experimental variogram
and the fitted variogram model
autofitVariogram
is mostly used indirectly through the function autoKrige
Paul Hiemstra, p.hiemstra@geo.uu.nl
fit.variogram
, autoKrige
, posPredictionInterval
data(meuse) coordinates(meuse) =~ x+y variogram = autofitVariogram(zinc~1,meuse) plot(variogram) # Residual variogram data(meuse) coordinates(meuse) =~ x+y variogram = autofitVariogram(zinc ~ soil + ffreq + dist, meuse) plot(variogram)