Basic GIS in R
in R / Software on Code, Example, Gis, R, Software
Recently I had to help out a colleague with processing some spatial data in R. The overall goal was to find landscape parameters (topography, soil characteristics, etc.) within the neighbourhood of a flux tower.
The below code gives a short introduction on how to extract data from both raster and shapefiles (vector data), very common operations . I will add more tips and tricks as I come across them.
# Load libraries.
# For raster data
require(raster)
# For vector data
require(sp)
# Set flux tower coordinates.
lat= 45.2041
lon=-68.7402
# Define lat / lon projection.
lat_lon <- CRS("+init=epsg:4326")
# Define UTM projection.
utm <- CRS( "+proj=utm +zone=19 +north +ellps=WGS84 +datum=WGS84 +no_defs")
# Read in the coordinates and assign them a projection, # otherwise they remain just 'numbers'
location <- SpatialPoints(cbind(lon,lat), lat_lon)
# Convert to utm using the above projection string
# using spTransform.
location_utm <- spTransform(location, utm)
# Load raster Digital Terrain Map (DTM) data.
# If the raster data has no projection,
# you will have to assign a projection.
# I assume the file has a projection.
dtm <- raster('DTM.tif')
# Relative height of the location of the tower.
dtm_data <- extract(dtm,location_utm)
# Read in soil shapefile.
soils <- readShapeSpatial("soils.shp")
# Assign projection to the soils.shp file
# if not provided.
proj4string(soils) <- utm
# Extract soil polygon attributes.
soil_attributes <- over(location_utm,soils)