Add length and area measures to flowpaths/divides

Computes `lengthkm` on flowpaths and `areasqkm` on divides, then joins each divide's incremental `areasqkm` onto its flowpath. Any `areasqkm` already on `flowpaths` is dropped first, so the returned value always comes from `divides`. The geometry column of both layers is renamed to `"geometry"`.

Usage

add_measures(flowpaths, divides)

Arguments

flowpaths

sf LINESTRING

divides

sf POLYGON

Value

named list of updated flowpaths and divides

Details

The divide-to-flowpath join prefers an explicit `flowpath_id` column on `divides`, which the current schema requires because `divide_id` and `flowpath_id` use different namespaces (`cat-*` vs `fp-*`). When `divides` carries no `flowpath_id`, the join falls back to the legacy 1:1 convention that `divide_id == flowpath_id`. Picking the wrong key here matches nothing and silently zeroes `areasqkm`, along with any total area accumulated from it, so a fabric whose divides lack `flowpath_id` under the current schema should be repaired rather than passed through this fallback.

See also

[add_lengthkm()], [add_areasqkm()]

Examples

if (FALSE) { # \dontrun{
fps <- sf::read_sf("hydrofabric.gpkg", "flowpaths")
divs <- sf::read_sf("hydrofabric.gpkg", "divides")
out <- add_measures(fps, divs)
out$flowpaths$lengthkm
} # }