R: fractal dimension

fractal.dim {RandomFields}

R Documentation

fractal dimension

Description

The function estimates the fractal dimension of a process

Usage

fractal.dim(x, y = NULL, z = NULL, data,
           grid=TRUE, gridtriple = FALSE,
           bin= seq(min(ct$x[3, ]) / 2, 
             min((ct$x[2,]-ct$x[1,]) / 4, vario.n * min(ct$x[3,]) + 1),
             min(ct$x[3,])),
           vario.n=5,
           sort=TRUE,
           fft.m = c(65, 86), ## in 
           fft.max.length=Inf,
           fft.max.regr=150000,
           fft.shift = 50, # in 
           method=c("variogram", "fft"), 
           mode=c("plot", "interactive"),
           pch=16, cex=0.2, cex.main=0.85,
           PrintLevel = RFparameters()$Print,
           height=3.5,
           ...)

Arguments

`x`	matrix of coordinates, or vector of x coordinates; if `x` is not given a grid with unit grid length is assumed
`y`	vector of y coordinates
`z`	vector of z coordinates
`data`	the values measured.
`grid`	determines whether the vectors `x`, `y`, and `z` should be interpreted as a grid definition, see Details. `grid` does not apply for `T`.
`gridtriple`	logical. Only relevant if `grid=TRUE`. If `gridtriple=TRUE` then `x`, `y`, and `z` are of the form `c(start,end,step)`; if `gridtriple=FALSE` then `x`, `y`, and `z` must be vectors of ascending values.
`bin`	sequence of bin boundaries for the empirical variogram
`vario.n`	first `vario.n` value of the empirical variogram are used for the regression fit that are not `NA`.
`sort`	If `TRUE` then the coordinates are permuted such that the largest grid length is in `x`-direction; this is of interest for algorithms that slice higher dimensional fields into one-dimensional sections.
`fft.m`	numeric vector of two components; interval of frequencies for which the regression should be calculated; the interval is given in percent of the range of the frequencies in log scale.
`fft.max.length`	The first dimension of the data is cut into pieces of length `fft.max.length`. For each piece the FFT is calculated and then the average for all pieces is taken. The pieces may overlap, see the parameter `fft.shift`.
`fft.max.regr`	If the `fft.m` is too large, parts of the regression fit will take a very long time. Therefore, the regression fit is calculated only if the number points given by `fft.m` is less than `fft.max.regr`.
`fft.shift`	This parameter is given in percent [of `fft.max.length`] and defines the overlap of the pieces defined by `fft.max.length`. If `fft.shift`=50 the WOSA estimator is given; if `fft.shift`=100 no overlap exist.
`method`	list of implemented methods to calculate the fractal dimension; see Details
`mode`	character. A vector with components 'nographics', 'plot', or 'interactive': 'nographics' no graphical output 'plot' the regression line is plotted 'interactive' the regression domain can be chosen interactively Usually only one mode is given. Two modes may make sense in the combination c("plot", "interactive") in which case all the results are plotted first, and then the interactive mode is called. In the interactive mode, the regression domain is chosen by two mouse clicks with the left mouse; a right mouse click leaves the plot.
`pch`	vector or scalar; sign by which data are plotted.
`cex`	vector or scalar; size of `pch`.
`cex.main`	The size of the title in the regression plots.
`PrintLevel`	integer. If `PrintLevel` is 0 nothing is printed. If `PrintLevel=1` error messages are printed. If `PrintLevel=2` warnings and the regression results are given. If `PrintLevel>2` tracing information is given.
`height`	height of the grahics window
`...`	graphical parameters

Details

The function calculates the fractal dimension by various methods:

variogram method
Fourier transform

Value

The function returns a list with elements vario, fft corresponding to the 2 methods given in the Details.
Each of the elements is itself a list that contains the following elements.

`x`	the x-coordinates used for the regression fit
`y`	the y-coordinates used for the regression fit
`regr`	the return list of the `lm`
`sm`	smoothed curve through the (x,y) points
`x.u`	`NULL` or the restricted x-coordinates given by the user in the interactive plot
`y.u`	`NULL` or y-coordinates according to `x.u`
`regr.u`	`NULL` or the return list of `lm` for `x.u` and `y.u`
`D`	the fractal dimension
`D.u`	`NULL` or the fractal dimension corresponding to the user's regression line

Author(s)

Martin Schlather, martin.schlather@math.uni-goettingen.de http://www.stochastik.math.uni-goettingen.de/institute

References

variogram method

Constantine, A.G. and Hall, P. (1994) Characterizing surface smoothness via estimation of effective fractal dimension. J. R. Statist. Soc. Ser. B 56, 97-113.

fft

Chan, Hall and Poskitt (1995)