Extract Raster Values at Hex Cell Centers

Samples raster values at hexagonal cell centers. Faster than hex_zonal() because it only queries cell center points, not full polygons.

Usage

hex_extract(raster, grid, cells = NULL, boundary = NULL)

Arguments

raster

A terra::SpatRaster object.

grid

A HexGridInfo or HexData object specifying the grid.

cells

Optional cell IDs to extract. If NULL (default), extracts at all cell centers from grid (only works for HexData objects or if a boundary is provided).

boundary

Optional sf polygon to limit extraction extent.

Value

A data.frame with columns cell_id, plus one column per raster layer.

Details

Requires the terra package (in Suggests). The function:

1. Generates cell centers for the raster extent

2. Calls terra::extract(raster, cell_center_matrix)

3. Attaches cell IDs

For full zonal statistics (aggregating all pixels within each hex polygon), use hex_zonal() instead.

See also

hex_zonal() for polygon-based zonal statistics, hexify() for creating HexData objects

Examples

# \donttest{
if (requireNamespace("terra", quietly = TRUE)) {
  # Create a small synthetic raster
  r <- terra::rast(nrows = 10, ncols = 10,
                   xmin = -10, xmax = 10, ymin = 40, ymax = 55)
  terra::values(r) <- runif(100)
  names(r) <- "temperature"

  # Extract at hex cell centers
  g <- hex_grid(area_km2 = 500)
  df <- data.frame(lon = c(0, 5), lat = c(45, 50))
  hd <- hexify(df, lon = "lon", lat = "lat", grid = g)
  hex_extract(r, hd)
}
# }