Spatial helpers for STAC documents — geom

Helper functions to derive the spatial metadata required by STAC items.

extract_bbox(): reads a raster (local or remote) and returns its bounding box in WGS84 (EPSG:4326). This function requires the optional terra package. It is generic: pass either a character path or URL, or a doc_asset from new_asset(), in which case the raster is read from the asset's resolved local_path (see update_root()) or its href.
as_geometry(): converts a bounding box into a GeoJSON Polygon geometry. This function has no external dependencies.

If terra is not installed, you can still build items by passing a bounding box (a numeric vector c(xmin, ymin, xmax, ymax)) directly to new_item() and, optionally, a geometry created with as_geometry().

Usage

extract_bbox(x)

# S3 method for class 'character'
extract_bbox(x)

# S3 method for class 'doc_asset'
extract_bbox(x)

as_geometry(bbox)

Arguments

x: A character path or URL to a raster file readable by terra, or a doc_asset from new_asset(). Remote http(s) URLs are accessed through GDAL's /vsicurl/ driver.
bbox: A numeric vector of length 4 with the bounding box coordinates in the order c(xmin, ymin, xmax, ymax).

Value

extract_bbox(): a numeric vector c(xmin, ymin, xmax, ymax), or NULL if the raster could not be read.
as_geometry(): a list representing a GeoJSON Polygon geometry, or NULL if bbox is NULL.

Examples

# as_geometry() works without any optional dependency
bbox <- c(-50, -10, -49, -9)
as_geometry(bbox)
#> <GeoJSON Geometry: Polygon>
#>   bbox: -50, -10, -49, -9

# extract_bbox() requires terra
if (requireNamespace("terra", quietly = TRUE)) {
  f <- system.file("extdata/s2/S2_MSI_20LMR_B04_2022-07-16.tif",
                    package = "rstatic")
  if (nzchar(f)) {
    # from a path or URL
    extract_bbox(f)
    # or directly from an asset
    extract_bbox(new_asset(f, title = "B04"))
  }
}
#>       xmin       ymin       xmax       ymax 
#> -63.636579  -8.630257 -63.418217  -8.412882