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

In csaybar/rgee: R Bindings for Calling the 'Earth Engine' API

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
)

Arguments

image	EE Image object to be converted into a stars object.
region	EE Geometry Rectangle (ee$Geometry$Rectangle) specifying the region to export.The CRS needs to be the same as the x argument, otherwise, it will be forced.
dimensions	Numeric vector of length 2. Thumbnail dimensions in pixel units. If a single integer is provided, it defines the size of the image's larger aspect dimension and scales the smaller dimension proportionally. Defaults to 512 pixels for the larger image aspect dimension.
vizparams	A list that contains 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 only is possible export 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 names to be mapped to 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 (DN) 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 images only)	comma-separated list of hex strings
opacity	The opacity of the layer (0.0 is fully transparent and 1.0 is fully opaque)	number

Value

An stars or Raster object depending on the raster argument.

See Also

Other image download functions: ee_as_raster(), ee_as_stars(), ee_imagecollection_to_local()

Examples

## Not run: 
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")

## End(Not run)

csaybar/rgee documentation built on March 11, 2021, 5:48 a.m.