Validates and prepares one drawn or terrain-derived Flowline. By default, DEM endpoint elevations orient it downstream-to-upstream. An explicit topology-preserving mode retains direction already established by a routed Stream Network.
flowline(flowline, reach_name, dem, direction = c("dem", "preserve"))sf object; One flowline with a defined CRS.
character; The name of the stream reach.
terra SpatRaster object; A DEM in the Flowline CRS. In
"dem" mode it supplies endpoint-elevation direction evidence; in
"preserve" mode it remains part of the shared preparation contract.
Character; "dem" retains the historical endpoint-elevation
orientation. "preserve" keeps an upstream-directed line whose direction
has already been established by saved network topology.
One sf Flowline with only ReachName and geometry fields. Its
coordinates begin downstream and end upstream when the selected direction
method supplies or preserves that evidence.
Uses orient_lines_from_dem() for endpoint-based upstream orientation
by default. direction = "preserve" is intended for linework whose
downstream-to-upstream direction is already established by topology; it
retains that direction while applying the same CRS, cardinality and output
field contract.
Browser-drawn WGS84/Web Mercator input retains the historical GeoJSON CRS
repair. Other explicitly defined projected CRSs pass through unchanged. If
direction cannot be resolved, returns unchanged linework with a warning.