inst/userguide/figures/CS5--Cs09b_GCDF.R

In nwfsc-timeseries/MARSS: Multivariate Autoregressive State-Space Modeling

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### code chunk number 12: Cs09b_GCDF
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GCDF <- function(lon1, lon2, lat1, lat2, degrees = TRUE, units = "miles") {
  temp <- ifelse(degrees == FALSE,
    acos(sin(lat1) * sin(lat2) + cos(lat1) * cos(lat2) * cos(lon2 - lon1)),
    acos(sin(lat1 / 57.2958) * sin(lat2 / 57.2958) +
      cos(lat1 / 57.2958) * cos(lat2 / 57.2958) *
        cos(lon2 / 57.2958 - lon1 / 57.2958))
  )
  r <- 3963.0 # (statute miles) , default
  if ("units" == "nm") r <- 3437.74677 # (nautical miles)
  if ("units" == "km") r <- 6378.7 # (kilometers)
  return(r * temp)
}