R/theta0.R

In Swarchal/phenoDist: Distance Measurements in Phenotypic Screening

#' norm of a vector
#'
#' @param x vector
    
 # length/norm of a vector 'x'
norm_vec <- function(x) sqrt(x %*% x)


#' Angle between a vector and the origin
#' 
#' Calculates the angle (in degrees) between a vector and the origin (1,0)
#' 
#' @param a Vector
#' @return Angle, in degrees
#' 
#' @export
#'
#' @examples
#' a <- c(1, 0)
#' theta0(a)
#' 
#' a <- c(-1, 0)
#' theta0(a)
#' 
#' a <- c(-1, -1)
#' theta0(a)

theta0 <- function(a){
    # computes the angle between a vector and the origin
    
    if (length(a) != 2){
        stop("input vector needs to have a length of 2")
    }
    
    # origin vector
    origin <- c(1, 0)
    
    theta <- as.vector(
        acos(a %*% origin / (norm_vec(a) * norm_vec(origin))) * 180/pi
        )
    
    # need to measure the angle from a set reference, so it's always anticlockwise
    # otherwise theta never exceed 180
    
    if (a[2] >= 0){
        return(theta)
    }
    
    if (a[2] <0){
        return(360 - theta)
    }

}

#' Angle between the vector and the origin
#'
#' Calculates and angle (in degrees) between the vector and the origin
#' \code{c(1, rep(0, length(vector) - 1))}
#'
#' @param a numeric vector
#' @export

theta0_ <- function(a){

    origin <- c(1, rep(0, (length(a) - 1)))
    stopifnot(length(a) == length(origin))
    as.vector(acos(a %*% origin / (norm_vec(a) * norm_vec(origin))) * 180/pi)
}