3. Integration of rgee with r-spatial ecosystem

3.1 Requeriments

library(rgee)
library(tmap)
library(raster)
library(viridis)
library(mapview)
library(cptcity)
ee_Initialize() # Initialize gee inside R with registered account

── rgee 1.1.5 ────────────────────────────────────────────────────── earthengine-api 0.1.334 ── 
 ✔ user: not_defined
 ✔ Initializing Google Earth Engine:  DONE!
 ✔ Earth Engine account: users/ambarja 
─────────────────────────────────────────────────────────────────────────────────────────────── 

3.2 Processing data with rgee

r_temp <- ee$ImageCollection$Dataset$ECMWF_ERA5_LAND_MONTHLY
ee_temp <- r_temp$
  select("temperature_2m")$
  filterDate("1992-01-01","1992-12-31")$
  mean()$
  subtract(273.15)

3.3 Simple visualization

viz_temp <- list(
  min = 5,
  max = 25,
  palette = magma(n = 100)
  )

temp <- Map$addLayer(ee_temp, visParams = viz_temp) + 
  Map$addLegend(visParams = viz_temp,name = "Tem[C°]",position = "bottomleft")

temp

3.4 Define box to study area

geometry <- ee$Geometry$Rectangle(
  coords = c(-180,-90,180,90),
  proj = "EPSG:4326",
  geodesic = FALSE
)

3.5 Identifying min and max values of temperature

(minmax <- ee_temp$reduceRegion(
  reducer = ee$Reducer$minMax(),
  geometry = geometry,
  scale = 500*1000)$
  getInfo())

$temperature_2m_max
[1] 29.68718
$temperature_2m_min
[1] -53.14849

3.6 Generate a thumbnail image in a rasterlayer or stars format

world_temp <- ee_as_thumbnail(
  image = ee_temp,     # Image to export
  region = geometry,   # Region of interest
  dimensions = 1024,   # output dimension
  raster = TRUE,       # If FALSE returns a stars object. FALSE by default
  vizparams = list(min = -53.14849, max = 29.68718)
)

3.7 Processing data for mapping with tmap

# Define a projection (EPSG:4326 - WGS 84)
crs(world_temp) <- 4326
world_temp[] <- scales::rescale(
  getValues(world_temp),
  c(minmax$temperature_2m_min, minmax$temperature_2m_max)
) 
# Load world vector (available after load tmap)
data("World") 
# Define a Robin type projection 
robin <- "+proj=robin +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs"
# Remove the temperature value of sea
map <-  world_temp %>% 
  mask(World) 

3.9 Elaboration of the Temperature Map

temp_map <- map %>% 
  tm_shape(projection = robin,raster.warp = FALSE) +
  tm_raster(
    title = "Temperature (°C)",
    palette = magma(n = 100),
    style = "cont"
  ) + 
  tm_shape(shp = World) + 
  tm_borders(col = "black",lwd = 0.7) + 
  tm_graticules(alpha = 0.8, lwd = 0.5, labels.size = 0.5)
temp_map

3.10 Export map in png format

tmap_save(temp_map,"temp_map.png",width = 6,height = 3)

3.11 Mapping of the current vegetation index

# Processing data with rgee
r_ndvi <- ee$ImageCollection$Dataset$MODIS_006_MYD13Q1
ee_ndvi <- r_ndvi$
  select("NDVI")$
  filterDate("2022-01-01","2022-01-31")$
  max()$
  multiply(0.0001)

3.12 Simple visualization

viz_ndvi <- list(
  min = -0.5 ,
  max = 0.87,
  palette = cpt(pal = "grass_ndvi")
  )
ndvi <- Map$addLayer(ee_ndvi,visParams = viz_ndvi) + 
  Map$addLegend(visParams = viz_ndvi,name = "NDVI")
ndvi