Calculate Distance and Speed Between GPS Points 
#This code was written by Leonardo Custode. 
>>library(sf) 
>>library(parallel) 
>>library(foreach) 
>>library(stringr) 
>>directory <- "~/Desktop/Cat Stuff/Cat GPS Tracks/2019catcamshapefiles/"  
>> outdirectory <-"~/Desktop/Cat Stuff/Cat GPS Tracks/Speed output 2019 Shapefiles/" 
>> list <- list.files(directory,pattern = "\\.shp$",full.names = TRUE)  #Creates a list of all shapefiles in the directory 
>> numCores <- detectCores() #detects the number of cores in the computer for multiprocessing 
>> registerDoParallel(numCores) #sets up dopar for multiprocessing 
>>foreach(i = 1:length(list))%dopar%{  #iterates through files equal to the number of cores in the computer simultaneously 
>>file <- st_read(list[i])  
>>file$distance <- NA  #creates a column called “distance which will store the distance from the last point in 
>>file$Timefrom <- NA # creates a column called “Timefrom” where the time elapsed between the last few points will be stored 
>>file$speed <- NA  #This column stores the speed the cat would have had to travel to get between these two points 
>>for(j in 1:nrow(file)){ #iterates through each point in the shapefile 
>> if(isTRUE(j == 1)){next}  #the first observation will not have previous observation so this skips it 
>>else if(isTRUE(j > 1)){ 
file[j,19] <- st_distance(file[j,],file[j-1,]) #calculates and stores the distance (m) between the current point and the previous point 
>> file[j,20] <-as.numeric(difftime(as.POSIXct(file[j,]$BeginTime), as.POSIXct(file[j-1,]$BeginTime),units = "secs")) #calculates and stores the time (s) between the current point and the previous point 
>>file[j,21] <- file[j,19]/file[j,20] #calculates and stores the speed the cat travelled between the current point and the previous point stored in m/s 
      } 
  } 
 >>#TooFast <- 1.6667 #rewrite this variable to be the speed considered to be too fast for a cat to realistically travel 
>>#TooFar <-  #set a distance that is considered to be too far for a cat to realistically travel 
>> #file <- file[file$speed < TooFast & distance > TooFar] 
>>fileout <- basename(list[i]) 
>>pathout <- str_c(outdirectory,fileout) 
>>file <- st_zm(file) 
>>st_write(file,pathout) #saves the new shapefile with distance, Timefrom, and speed 
}