rgee (version 0.2.0)

ee_as_thumbnail: Create a stars object based on an EE thumbnail image

Description

Download EE thumbnail images and read them as stars objects. This function is a wrapper around ee$Image()$getThumbURL().

Usage

ee_as_thumbnail(x, region, dimensions, vizparams = NULL, crs = 4326,
  quiet = FALSE)

Arguments

x

EE Image object

region

EE Geometry Rectangle (ee$Geometry$Rectangle)

dimensions

A number or pair of numbers in format XY.

vizparams

A list that contains the visualization parameters.

crs

The EE Image projection e.g. 'EPSG:3857'. WGS84 by default ('EPSG:4326').

quiet

logical; suppress info messages.

Value

An sf object

Details

The argument dimensions will define the stars object parameters "from" & "to". It must be a single numeric value or a two-element vector. If not defined, 256 is taken by default as the dimension of x (from 1 to 256), and y scales down proportionally. Huge images might cause plodding connections. See Client vs Server for more details.

The vizparams set up the number of bands up. In ee_as_thumbnail just is possible export only one (G) or three-band (RGB) images. Additional parameters can be passed on to control color, intensity, the maximum and minimum values, etc. The below table 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

Use ee$Image()$geometry()$projection()$crs()$getInfo() for getting the CRS of an Earth Engine Image.

Examples

# NOT RUN {
library(rgee)
library(stars)

ee_reattach() # reattach ee as a reserved word
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"
)
ndvi_palette <- c(
  "#FC8D59", "#FC8D59", "#FC9964", "#FED89C", "#FFFFBF",
  "#FFFFBF", "#DAEF9F", "#9DD46A", "#91CF60", "#91CF60"
)
# Example 01  - SRTM AREQUIPA-PERU
image <- ee$Image("CGIAR/SRTM90_V4")
region <- nc$geometry[[1]] %>%
  st_bbox() %>%
  st_as_sfc() %>%
  st_set_crs(4326) %>%
  sf_as_ee()

arequipa_dem <- ee_as_thumbnail(x = image, region = region,
                                vizparams = list(min = 0, max = 5000))
arequipa_dem <- arequipa_dem * 5000

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))
# }