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Satellite imagery from STAC catalogues

geo-stac.Rd

Search and read satellite imagery from any STAC API (SpatioTemporal Asset Catalog), such as Element 84 Earth Search, which serves Sentinel-2, Landsat and Copernicus DEM data as cloud-optimised GeoTIFFs:

  • geo_stac_collections() lists the collections a catalogue offers.

  • geo_stac_search() finds the scenes of a collection over an area and a period, with a cloud cover limit, and returns their footprints as an sf table, clearest first.

  • geo_stac_read() reads chosen bands of those scenes into a SpatRaster. Only the window over your area is downloaded (GDAL reads cloud-optimised GeoTIFFs over HTTP), the scale and offset stored in the catalogue are applied, so Sentinel-2 bands come out as surface reflectance from 0 to about 1 (negative values from the offset are set to 0), and several scenes are combined into a per-pixel median, which removes most clouds.

The result goes straight into geo_spectral_index(), geo_spectral_diversity() or map_raster().

Usage

geo_stac_collections(url = tmr_stac_default)

geo_stac_search(
  collection,
  area,
  datetime = NULL,
  cloud_cover = 20,
  limit = 50,
  url = tmr_stac_default
)

geo_stac_read(items, assets, area = NULL, n = 1, crs = NULL, scale = TRUE)

Arguments

url

Root URL of a STAC API. Default: Element 84 Earth Search.

collection

Collection id, for example "sentinel-2-l2a", "landsat-c2-l2" or "cop-dem-glo-30".

area

Area of interest: an sf or terra object, or c(xmin, ymin, xmax, ymax) in degrees.

datetime

Period: two dates (c("2024-06-01", "2024-08-31")) or one.

cloud_cover

Largest cloud cover (percent) to accept; NULL for collections without cloud cover.

limit

Largest number of scenes to return.

items

Scenes from geo_stac_search().

assets

Bands to read, by asset name, for example c("red", "nir") for Sentinel-2 on Earth Search.

n

Number of scenes to combine (the clearest first). One scene is read as is; several are combined into the per-pixel median.

crs

Coordinate reference system of the result; by default that of the first scene.

scale

Apply the scale and offset stored in the catalogue?

Value

geo_stac_collections(): a tibble of id, title. geo_stac_search(): an sf table with one row per scene (id, datetime, cloud_cover, platform, assets). geo_stac_read(): a SpatRaster with one layer per asset.

See also

geo_spectral_index(), map_raster().

Examples

if (FALSE) { # interactive() && rlang::is_installed(c("httr2", "terra", "sf"))
# Sentinel-2 over Luxembourg City, summer 2024
lux <- c(6.08, 49.57, 6.18, 49.65)
scenes <- geo_stac_search("sentinel-2-l2a", lux,
  datetime = c("2024-06-01", "2024-08-31"), cloud_cover = 10
)
scenes
img <- geo_stac_read(scenes, c("red", "nir"), area = lux, n = 3)
ndvi <- geo_spectral_index(img, "NDVI")
geo_map(title = "NDVI, Luxembourg City, summer 2024") |>
  map_raster(ndvi, name = "NDVI", palette = "Greens 3")
}