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Enforce upstream->downstream orientation on aggregated flowpath geometry

Source: R/enforce_flowpath_flowdir.R
enforce_flowpath_flowdir.Rd

extend_flowpaths_to_mainstem() rebuilds each aggregate flowpath line with geos_line_merge, which does not preserve flow direction, and (unlike the reconciled flowlines, guarded by the reconciled_flow_direction invariant) the aggregated flowpaths layer has no orientation check, so a fraction of flowpaths ship reversed (their geometry runs downstream->upstream). This pass re-orients every flowpath so its OUTLET is the LAST vertex.

The true outlet is located from the reliably-oriented flowlines layer: each flowpath's outlet sub-flowline is the member whose flowline_toid leaves the flowpath, and its downstream (end) vertex is the flowpath outlet. A flowpath whose START is nearer that outlet than its END is reversed and is flipped with sf::st_reverse(). Genuinely branching multi-part geometry (no single meaningful direction) is left untouched.

Usage

enforce_flowpath_flowdir(
  gpkg,
  flowpath_layer = "flowpaths",
  flowlines_layer = "flowlines"
)

Arguments

gpkg

Path to a GeoPackage containing flowpath_layer and flowlines_layer.

flowpath_layer, flowlines_layer

Layer names. Defaults "flowpaths" / "flowlines".

Value

Invisibly, the number of flowpaths reversed. Overwrites flowpath_layer in place.

Examples

if (FALSE) { # \dontrun{
enforce_flowpath_flowdir("ngen_vpu01.gpkg")
} # }