R/splitLine.R

In JorGarMol/VoCC: The Velocity of Climate Change and related climatic metrics

#' Internal. Split a line segment defined by points A-B into n parts
#' @param A \code{numeric} giving coordinates of first point
#' @param B \code{numeric} giving coordinates of second point
#' @param n \code{numeric} number of segments to divide the distance between points with
#' @author Jorge Garcia Molinos
#' @rdname splitLine

splitLine <- function(A, B, n){
# Remove sign change for dateline, if needed
B[,1] <- with(B, ifelse(abs(B[,1]-A[,1]) > 180 &  B[,1] < 0 , B[,1] + 360, B[,1]))
A[,1] <- with(A, ifelse(abs(B[,1]-A[,1]) > 180 &  A[,1] < 0 , A[,1] + 360, A[,1]))

xstp <- (B[,1] - A[,1])/n
ystp <- (B[,2] - A[,2])/n

if(length(xstp)>1){
Points <- mapply(function(X, Y, xstp, ystp, n) {
x <- as.numeric(X) + (as.numeric(xstp)*(0:n))
# Adjust for dateline jumps / return to -180o to 180o format
x <- x - (360 * floor((x + 180) / 360))
y <- as.numeric(Y) + (as.numeric(ystp)*(0:n))
do.call(cbind, list(x,y))
}, A[,1], A[,2], xstp, ystp, n, SIMPLIFY = FALSE)
}
# if there is only 1 trajectory active no need for mapply
if(length(xstp) == 1){
x <- A[,1] + (xstp*(0:n))
# Adjust for dateline jumps / return to -180o to 180o format
x <- x - (360 * floor((x + 180) / 360))
y <- A[,2] + (ystp*(0:n))
Points <- cbind(x,y)
}
return(Points)
}