ee_as_thumbnail: Create an R spatial gridded object from an EE thumbnail image

Description

Wrapper function around ee$Image$getThumbURL to create a stars or RasterLayer R object from a EE thumbnail image.

Usage

ee_as_thumbnail(
  image,
  region,
  dimensions,
  vizparams = NULL,
  raster = FALSE,
  quiet = FALSE
)

Value

An stars or Raster object depending on the raster argument.

Arguments

image: EE Image object to be converted into a stars object.
region: EE Geometry Rectangle (ee$Geometry$Rectangle) specifies the region to be exported. The CRS must match the 'x' argument; otherwise, it will be forced.
dimensions: Numeric vector of length 2 that specifies the dimensions of the thumbnail image in pixels. If only one integer is provided, it determines the size of the larger dimension of the image and scales the other dimension proportionally. Defaults to 512 pixels for the larger image aspect dimension.
vizparams: A list containing the visualization parameters.See details.
raster: Logical. Should the thumbnail image be saved as a RasterStack object?
quiet: logical; suppress info messages.

Details

vizparams set up the details of the thumbnail image. With ee_as_thumbnail allows exporting only one-band (G) or three-band (RGB) images. Several parameters can be passed on to control color, intensity, the maximum and minimum values, etc. The table below provides all the parameters that admit ee_as_thumbnail.

Parameter	Description	Type
bands	Comma-delimited list of three band (RGB)	list
min	Value(s) to map to 0	number or list of three numbers, one for each band
max	Value(s) to map to 1	number or list of three numbers, one for each band
gain	Value(s) by which to multiply each pixel value	number or list of three numbers, one for each band
bias	Value(s) to add to each Digital Number value	number or list of three numbers, one for each band
gamma	Gamma correction factor(s)	number or list of three numbers, one for each band
palette	List of CSS-style color strings (single-band only)	comma-separated list of hex strings
opacity	The opacity of the layer (from 0 to 1)	number

Examples

Run this code

if (FALSE) {
library(raster)
library(stars)
library(rgee)

ee_Initialize()

nc <- st_read(system.file("shp/arequipa.shp", package = "rgee"))
dem_palette <- c(
  "#008435", "#1CAC17", "#48D00C", "#B3E34B", "#F4E467",
  "#F4C84E", "#D59F3C", "#A36D2D", "#C6A889", "#FFFFFF"
)

## DEM data -SRTM v4.0
image <- ee$Image("CGIAR/SRTM90_V4")
world_region <- ee$Geometry$Rectangle(
  coords = c(-180,-60,180,60),
  proj = "EPSG:4326",
  geodesic = FALSE
)

## world - elevation
world_dem <- ee_as_thumbnail(
  image = image,
  region = world_region,
  dimensions = 1024,
  vizparams = list(min = 0, max = 5000)
)

world_dem[world_dem <= 0] <- NA
world_dem <- world_dem * 5000

plot(
  x = world_dem, col = dem_palette, breaks = "equal",
  reset = FALSE, main = "SRTM - World"
)

## Arequipa-Peru
arequipa_region <- nc %>%
  st_bbox() %>%
  st_as_sfc() %>%
  sf_as_ee()

arequipa_dem <- ee_as_thumbnail(
  image = image,
  region = arequipa_region$buffer(1000)$bounds(),
  dimensions = 512,
  vizparams = list(min = 0, max = 5000)
)

arequipa_dem <- arequipa_dem * 5000
st_crs(arequipa_dem) <- 4326
plot(
  x = arequipa_dem[nc], col = dem_palette, breaks = "equal",
  reset = FALSE, main = "SRTM - Arequipa"
)

suppressWarnings(plot(
  x = nc, col = NA, border = "black", add = TRUE,
  lwd = 1.5
))
dev.off()

## LANDSAT 8
img <- ee$Image("LANDSAT/LC08/C01/T1_SR/LC08_038029_20180810")$
  select(c("B4", "B3", "B2"))
Map$centerObject(img)
Map$addLayer(img, list(min = 0, max = 5000, gamma = 1.5))

## Teton Wilderness
l8_img <- ee_as_thumbnail(
  image = img,
  region = img$geometry()$bounds(),
  dimensions = 1024,
  vizparams = list(min = 0, max = 5000, gamma = 1.5),
  raster = TRUE
)
crs(l8_img) <- "+proj=longlat +datum=WGS84 +no_defs"
plotRGB(l8_img, stretch = "lin")
}