View source: R/spline-correlog2D.R
spline.correlog2D | R Documentation |
spline.correlog2D
is the function to estimate the anisotropic nonparametric correlation function in 8 (or arbitrary) directions (North - Southeast) for univariate data. Correlation functions are calculated for each different bearing. The function assumes univariate observations at each location. (use Sncf2D
otherwise).
spline.correlog2D( x, y, z, w = NULL, df = NULL, type = "boot", resamp = 1000, npoints = 300, save = FALSE, max.it = 25, xmax = FALSE, na.rm = FALSE, jitter = FALSE, quiet = FALSE, angle = c(0, 22.5, 45, 67.5, 90, 112.5, 135, 157.5) )
x |
vector of length n representing the x coordinates. |
y |
vector of length n representing the y coordinates. |
z |
vector of length n representing the observation at each location. |
w |
an optional second vector of length n for variable 2 (to estimate spatial or lagged cross-correlation functions). |
df |
degrees-of-freedom for the spline. Default is sqrt(n). |
type |
takes the value "boot" (default) to generate a bootstrap distribution or "perm" to generate a null distribution for the estimator |
resamp |
the number of resamples for the bootstrap or the null distribution. |
npoints |
the number of points at which to save the value for the spline function (and confidence envelope / null distribution). |
save |
If TRUE, the whole matrix of output from the resampling is saved (an resamp x npoints dimensional matrix). |
max.it |
the maximum iteration for the Newton method used to estimate the intercepts. |
xmax |
If FALSE, the max observed in the data is used. Otherwise all distances greater than xmax is omitted. |
na.rm |
If TRUE, NA's will be dealt with through pairwise deletion of missing values for each pair of time series – it will dump if any one pair has less than two (temporally) overlapping observations. |
jitter |
If TRUE, jitters the distance matrix to avoid problems associated with fitting the function to data on regular grids. |
quiet |
If TRUE, the counter is suppressed during execution. |
angle |
specifies number of cardinal directions and angles for which to calculate correlation functions. Default are 8 directions between 0 and 180. |
see Sncf2D
An object of class "Sncf2D" is returned. See Sncf2D
for details.
The function to estimate the UNIvariate anisotropic nonparametric (cross-)correlation function in arbitrary directions. In particular it was developed to calculate the univariate lagged cross-correlation function used in (Humston et al. 2005). Note that this 2D spline correlogram does the anisotropic analysis NOT by doing the angle-with-tolerance-wedge-style of Oden and Sokal (1986) but by projecting the the spatial coordinates of all locations on a sequence of cardinal angles (a la Sncf2D). Hence, all data points are used every time, it is only their relative distances that are changed. For example {0, 0} and {0, 10} are distance zero in the zero-degree direction but at distance 10 in the 90-degree direction.
Oden, N.L. and Sokal, R.R. 1986. Directional autocorrelation: an extension of spatial correlograms to two dimensions. Systematic Zoology 35: 608-617. <doi:10.2307/2413120> @references Humston, R., Mortensen, D. and Bjornstad, O.N. 2005. Anthropogenic forcing on the spatial dynamics of an agricultural weed: the case of the common sunflower. Journal of Applied Ecology 42: 863-872. <doi:10.1111/j.1365-2664.2005.01066.x>
Sncf2D
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