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Efficiently retrieve OCS GE data from a remote FlatGeobuf

get_ocsge_data_fgb.Rd

This function retrieves OCS GE (Land Cover) data for a specific Region of Interest (ROI) directly from a remote FlatGeobuf (.fgb) file hosted on a server (e.g., S3).

It leverages GDAL's virtual file system (`/vsicurl/`) and the spatial indexing capabilities of FlatGeobuf to download only the data chunks intersecting the bounding box of the ROI, making it highly efficient for large datasets.

Usage

get_ocsge_data_fgb(roi, fgb_url)

Arguments

roi

An sf object defining the Region Of Interest. It can be in any projection, but will be transformed to EPSG:2154 (Lambert-93) internally.

fgb_url

Character string. The public URL to the remote `.fgb` file.

Value

An sf object containing the OCS GE polygons intersected by the ROI, projected in Lambert-93 (EPSG:2154).

Details

The function performs the following steps:

  1. Transforms the roi to Lambert-93 (EPSG:2154).

  2. calculates the bounding box of the roi.

  3. Uses sf::st_read with a WKT filter to fetch only relevant features from the remote file.

  4. Applies a precise geometric intersection (`st_intersection`) to clip the data to the exact shape of the roi.

Note

This function requires a working internet connection and GDAL support for the FlatGeobuf driver and network capabilities (vsicurl).

Examples

if (FALSE) { # \dontrun{
  library(sf)

  # 1. Define a Region of Interest (ROI)
  # Example: A small bounding box in France
  my_roi <- st_as_sf(data.frame(
    lon = c(2.3, 2.4, 2.4, 2.3, 2.3),
    lat = c(48.8, 48.8, 48.9, 48.9, 48.8)
  ), coords = c("lon", "lat"), crs = 4326)

  # 2. URL to the remote FlatGeobuf file
  # (Replace with the actual URL of your OCS GE bucket)
  url_fgb <- "https://example.com/data/ocsge_grand_est.fgb"

  # 3. Fetch data
  ocsge_data <- get_ocsge_data_fgb(roi = my_roi, fgb_url = url_fgb)

  # 4. Check result
  print(ocsge_data)
  plot(st_geometry(ocsge_data))
} # }