R/EndCoordinates.R

In seantuck12/MODISTools: MODIS Subsetting Tools

EndCoordinates <- 
function(LoadDat, FileSep = NULL, Distance = 1000, Angle = 90, AngleUnits = 'radians'|'degrees', Dir = ".", 
         FileName = "Transect Coordinates")
{
  if(!is.object(LoadDat) & !is.character(LoadDat)) stop("Data must be the name of an object in R, or a file path.")
  if(is.object(LoadDat)) x <- data.frame(LoadDat)
  
  if(is.character(LoadDat)){
    if(!file.exists(LoadDat)) stop("Character string input for LoadDat argument does not resemble an existing file path.")
    if(is.null(FileSep)) stop("Data is a file path. Must also specify its delimiter (FileSep).")
    x <- read.delim(LoadDat, sep = FileSep) 
  }
  
  if(!file.exists(Dir)) stop("Character string input for Dir argument does not resemble an existing file path.")
    
  if(AngleUnits == 'radians' & Angle > (2 * pi)) stop('Not sensible radian values. Did you mean degrees?')
  if(AngleUnits == 'degrees' & Angle > 360) stop('Not sensible degrees values. Check input.')
    
  if(AngleUnits == 'radians') angle.rad <- Angle
  if(AngleUnits == 'degrees') angle.rad <- Angle / (180 / pi)
  
	lat.rad <- x$start.lat / (180 / pi)
	delta.lat.metres <- round(Distance * cos(angle.rad))
	delta.long.metres <- round(Distance * sin(angle.rad))
	delta.lat.degrees <- delta.lat.metres / (111.2 * 1000)
	delta.long.degrees <- delta.long.metres / ((111.2 * 1000) * cos(lat.rad))
	end.lat <- x$start.lat + delta.lat.degrees
	end.long <- x$start.long + delta.long.degrees
	x <- cbind(x, end.lat, end.long)
	
  write.csv(x, file = paste(Dir, "/", FileName, Distance, "m", Angle, AngleUnits, Sys.Date(), ".csv", sep = ""),
            row.names = FALSE)
}