Covariance functions of GRFs

Calculate values of the covariance function with geoR::cov.spatial():

sigma2 <- 1
phi <- 0.2
tibble::tibble(
  distance = seq(0, 1, 0.2),
  covariance_1 = cov.spatial(
    distance, 
    cov.pars = c(sigma2, phi),
    cov.model = "matern",
    kappa = 0.5 # default
  ),
  covariance_2 = cov.spatial(
    distance, 
    cov.pars = c(sigma2, phi),
    cov.model = "matern",
    kappa = 10
  )
)

## # A tibble: 6 × 3
##   distance covariance_1 covariance_2
##      <dbl>        <dbl>        <dbl>
## 1      0        1              1    
## 2      0.2      0.368          0.973
## 3      0.4      0.135          0.896
## 4      0.6      0.0498         0.782
## 5      0.8      0.0183         0.649
## 6      1        0.00674        0.513