R/TurningAngle.R

In abfleishman/trakR: Basic Animal Tracking Data Analysis Tools

#' Calculate the turning angles between points on a track for each bird
#'
#' @author Abram B. Fleishman \email{abram@@conservationmetrics.com}
#' @param tracks data.frame of data to be queried for  latand long values
#' @param ID quoted name of column in data that is and ID field
#' @param Bearing quoted name of column in data that has the bearing between points in an animal track
#' @importFrom dplyr lag
#' @return A vector of turning angles (degrees) between adjacent points in an animal track
#' @export
TurningAngle<-function(tracks,ID="File", Bearing="PointBearing"){
  dataOut<-NULL
  Birds<-unique(tracks[[ID]])
  for(i in 1:length(Birds)){
    Data<-tracks[tracks[[ID]]==Birds[i],]

    TurnAngle<-lag(Data[[Bearing]])-Data[[Bearing]]

    TurnAngle[TurnAngle>180&!is.na(TurnAngle)]<-TurnAngle[TurnAngle>180&!is.na(TurnAngle)]-360
    TurnAngle[TurnAngle< -180&!is.na(TurnAngle)]<-TurnAngle[TurnAngle< -180&!is.na(TurnAngle)]+360

    dataOut<-c(dataOut,TurnAngle)
  }
  return(dataOut)
}