Convert between geojson and sp spatial objects in R

convert_sp_geojson.r

# Convert between geojson and sp spatial objects in R
require(rgdal)

# https://stat.duke.edu/~cr173/Sta523_Fa14/spatial_data.html
s <- '{ "type": "MultiPolygon", "coordinates": [
  [ [[40, 40], [20, 45], [45, 30], [40, 40]] ], 
  [ [[20, 35], [10, 30], [10, 10], [30, 5], [45, 20], [20, 35]],
    [[30, 20], [20, 15], [20, 25], [30, 20]] 
  ]
]}'

spatialPolygon <- readOGR(s, "OGRGeoJSON", verbose = F, p4s = '+init=epsg:4326')
#plot(spatialPolygon, axes=TRUE)

spToGeoJSON <- function(x){
  # Return sp spatial object as geojson by writing a temporary file.
  # It seems the only way to convert sp objects to geojson is 
  # to write a file with OGCGeoJSON driver and read the file back in.
  # The R process must be allowed to write and delete temporoary files.
  #tf<-tempfile('tmp',fileext = '.geojson')
  tf<-tempfile()
  writeOGR(x, tf,layer = "geojson", driver = "GeoJSON")
  js <- paste(readLines(tf), collapse=" ")
  file.remove(tf)
  return(js)
}

js <- spToGeoJSON(spatialPolygon)
readOGR(js, "OGRGeoJSON", verbose = F, p4s = '+init=epsg:4326')