https://github.com/cran/fields
Tip revision: 04279c16ce718b82025aae97f6fcd30ba3a8b1c5 authored by Doug Nychka on 05 September 2011, 20:18:33 UTC
version 6.6
version 6.6
Tip revision: 04279c1
exp.image.cov.R
# fields, Tools for spatial data
# Copyright 2004-2011, Institute for Mathematics Applied Geosciences
# University Corporation for Atmospheric Research
# Licensed under the GPL -- www.gpl.org/licenses/gpl.html
"Exp.image.cov" <- function(ind1, ind2, Y, cov.obj = NULL,
setup = FALSE, grid, ...) {
if (is.null(cov.obj)) {
dx <- grid$x[2] - grid$x[1]
dy <- grid$y[2] - grid$y[1]
m <- length(grid$x)
n <- length(grid$y)
M <- ceiling2(2 * m)
N <- ceiling2(2 * n)
xg <- make.surface.grid(list((1:M) * dx, (1:N) * dy))
center <- matrix(c((dx * M)/2, (dy * N)/2), nrow = 1,
ncol = 2)
out <- Exp.cov(xg, center, ...)
out <- as.surface(xg, c(out))$z
temp <- matrix(0, nrow = M, ncol = N)
temp[M/2, N/2] <- 1
wght <- fft(out)/(fft(temp) * M * N)
cov.obj <- list(m = m, n = n, grid = grid, N = N, M = M,
wght = wght, call = match.call())
if (setup) {
return(cov.obj)
}
}
temp <- matrix(0, nrow = cov.obj$M, ncol = cov.obj$N)
if (missing(ind1)) {
temp[1:cov.obj$m, 1:cov.obj$n] <- Y
Re(fft(fft(temp) * cov.obj$wght, inverse = TRUE)[1:cov.obj$m,
1:cov.obj$n])
}
else {
if (missing(ind2)) {
temp[ind1] <- Y
}
else {
temp[ind2] <- Y
}
Re(fft(fft(temp) * cov.obj$wght, inverse = TRUE)[ind1])
}
}