Accumulated cost distance from stream cells — fl_cost

Computes the least-cost distance from every cell to the nearest stream cell, accumulating friction (typically slope) along the path. Stream cells are seed points with cost zero.

Usage

fl_cost_distance(friction, streams)

Arguments

friction: A SpatRaster of movement cost per cell (e.g., percent slope). Higher values = harder to traverse.
streams: A SpatRaster of rasterized streams (output of fl_stream_rasterize()). Any non-NA cell is treated as a seed point.

Value

A SpatRaster of accumulated cost distance. Stream cells have value 0; other cells increase with cost-weighted distance from the nearest stream.

Details

Uses terra::costDist() which implements a push-broom algorithm for weighted distance. The friction raster defines per-cell traversal cost and streams identifies seed cells (cost = 0).

Cells that are NA in friction are impassable barriers.

Examples

dem <- terra::rast(system.file("testdata/dem.tif", package = "flooded"))
slope <- terra::rast(system.file("testdata/slope.tif", package = "flooded"))
streams <- sf::st_read(
  system.file("testdata/streams.gpkg", package = "flooded"),
  quiet = TRUE
)
stream_r <- fl_stream_rasterize(streams, dem, field = "upstream_area_ha")
cost <- fl_cost_distance(slope, stream_r)
terra::plot(cost, main = "Cost distance from streams", range = c(0, 5000))