twTransfrom

twTransform.r

# install sp package before use
# read coordinates csv
twTransform <- function(input = file.choose(), x='x', y='y' ,from = 'wgs84', to= 'twd97'){
  require(sp)
  coords <- read.csv(input, sep = ',')
  coords <- cbind(coords[x], coords[y])
  colnames(coords) <- c('x', 'y')
  pts <- coordinates(coords)
  # projection
  wgs84 <- CRS('+proj=longlat +ellps=WGS84')
  twd97 <- CRS('+proj=tmerc +lat_0=0 +lon_0=121 +k=0.9999 +x_0=250000 +y_0=0 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs ')
  twd67 <- CRS('+proj=tmerc +lat_0=0 +lon_0=121 +k=0.9999 +x_0=250000 +y_0=0 +ellps=aust_SA +units=m +no_defs ')
  # Set projection
  if ( from == 'wgs84'){
    pts.prj <- SpatialPoints(pts, wgs84)
  } else if ( from == 'twd97' ){
    pts.prj <- SpatialPoints(pts, twd97)
  } else if ( from == 'twd67' ){
    pts.prj <- SpatialPoints(pts, twd67)
  } else {
    print('Please use wgs84, twd97 or twd67')
  }
  # transform to 
  if ( to == 'wgs84'){
    pts.reproj <- spTransform(pts.prj, wgs84)
  } else if ( from == 'twd97' ){
    pts.reproj <- spTransform(pts.prj, twd97)
  } else if ( from == 'twd67' ){
    pts.reproj <- spTransform(pts.prj, twd67)
  } else {
    print('Please use wgs84, twd97 or twd67')
  }
  pts.reproj.coords <- as.data.table(pts.reproj)
  return(pts.reproj.coords)
}

# call function
twTransform('/tmp/observations-24196.csv', x = 'longitude', y = 'latitude')