ee_as_stars: Convert an Earth Engine (EE) image in a stars object

Description

Convert an ee$Image in a stars object.

Usage

ee_as_stars(
  image,
  region = NULL,
  dsn = NULL,
  via = "drive",
  container = "rgee_backup",
  scale = NULL,
  maxPixels = 1e+09,
  grid_batch = 1024 * 1024,
  lazy = FALSE,
  public = FALSE,
  add_metadata = TRUE,
  timePrefix = TRUE,
  quiet = FALSE,
  ...
)

Value

A stars-proxy object

Arguments

image: ee$Image to be converted into a 'stars' object.
region: EE Geometry (ee$Geometry$Polygon) that specifies the region to export. CRS needs to be the same that the argument image. Otherwise, it will be forced. If not specified, image bounds are taken.
dsn: Character. Output filename. If missing, a temporary file is created.
via: Character. Method to export the image. Three methods are available: "getDownloadURL", "drive", "gcs". For "drive" and "gcs" see details. Use "getDownloadURL" for small images. Default "getDownloadURL".
container: Character. Name of the folder ('drive') or bucket ('gcs') to be exported.
scale: Numeric. Image resolution given in meters per pixel. Defaults to the native resolution of the image.
maxPixels: Numeric. The maximum allowable number of pixels in the exported image. If the exported region covers more pixels than the specified limit in the given projection, the task will fail. Defaults to 100,000,000.
grid_batch: Numeric. Argument used if 'via' is set as "getDownloadURL". The number of pixels to download in each batch without considering the number of bands. Default to 1048576 -(1024*1024).
lazy: Logical. If TRUE, a future::sequential object is created to evaluate the task in the future. See details.
public: Logical. If TRUE, a public link to the image is created.
add_metadata: Add metadata to the stars_proxy object. See details.
timePrefix: Logical. Add current date and time (Sys.time()) as a prefix to export files. This parameter helps to avoid exported files with the same name. By default TRUE.
quiet: Logical. Suppress info message
...: Extra exporting argument. See ee_image_to_drive and ee_image_to_gcs.

Details

ee_as_stars supports the download of ee$Images by two different options: "drive" (Google Drive) and "gcs" ( Google Cloud Storage). In both cases, ee_as_stars works as follow:

1. A task is started (i.e. ee$batch$Task$start()) to move the ee$Image from Earth Engine to the intermediate container specified in the argument via.
2. If the argument lazy is TRUE, the task will not be monitored. This is useful to lunch several tasks simultaneously and calls them later using ee_utils_future_value or future::value. At the end of this step, the ee$Image is stored on the path specified in the argument dsn.
3. Finally, if the argument add_metadata is TRUE, a list with the following elements is added to the stars-proxy object.
- if via is "drive":
  - ee_id: Name of the Earth Engine task.
  - drive_name: Name of the Image in Google Drive.
  - drive_id: Id of the Image in Google Drive.
  - drive_download_link: Download link to the image.
- if via is "gcs":
  - ee_id: Name of the Earth Engine task.
  - gcs_name: Name of the Image in Google Cloud Storage.
  - gcs_bucket: Name of the bucket.
  - gcs_fileFormat: Format of the image.
  - gcs_public_link: Download link to the image.
  - gcs_URI: gs:// link to the image.
Run attr(stars, "metadata") to get the list.

For getting more information about exporting data from Earth Engine, take a look at the Google Earth Engine Guide - Export data.

Examples

Run this code

if (FALSE) {
library(rgee)

ee_Initialize(drive = TRUE, gcs = TRUE)
ee_user_info()

# Define an image.
img <- ee$Image("LANDSAT/LC08/C01/T1_SR/LC08_038029_20180810")$
  select(c("B4", "B3", "B2"))$
  divide(10000)

# OPTIONAL display it using Map
Map$centerObject(eeObject = img)
Map$addLayer(eeObject = img, visParams = list(max = 0.4,gamma=0.1))

# Define an area of interest.
geometry <- ee$Geometry$Rectangle(
  coords = c(-110.8, 44.6, -110.6, 44.7),
  proj = "EPSG:4326",
  geodesic = FALSE
)

## getDownloadURL - Method 01 (for small images)
img_02 <- ee_as_stars(
  image = img,
  region = geometry,
  scale = 10
)

## drive - Method 02
# Simple
img_02 <- ee_as_stars(
  image = img,
  region = geometry,
  via = "drive"
)

# Lazy
img_02 <- ee_as_stars(
  image = img,
  region = geometry,
  via = "drive",
  lazy = TRUE
)

img_02_result <- img_02 %>% ee_utils_future_value()
attr(img_02_result, "metadata") # metadata

## gcs - Method 03
# Simple
img_03 <- ee_as_stars(
  image = img,
  region = geometry,
  container = "rgee_dev",
  via = "gcs"
)

# Lazy
img_03 <- ee_as_stars(
  image = img,
  region = geometry,
  container = "rgee_dev",
  lazy = TRUE,
  via = "gcs"
)

img_03_result <- img_03 %>% ee_utils_future_value()
attr(img_03_result, "metadata") # metadata

# OPTIONAL: clean containers
# ee_clean_container(name = "rgee_backup", type = "drive")
# ee_clean_container(name = "rgee_dev", type = "gcs")
}