Snap a Point to the Nearest FWA Stream

Snaps x/y coordinates to the nearest stream segment. When no blue_line_key is given, wraps fwapg fwa_indexpoint(). When blue_line_key is provided, uses KNN against fwa_stream_networks_sp filtered to that stream, with measure derivation and boundary clamping (following the bcfishpass pattern).

Usage

frs_point_snap(
  conn,
  x,
  y,
  srid = 4326L,
  tolerance = 5000,
  num_features = 1L,
  blue_line_key = NULL,
  stream_order_min = NULL
)

Arguments

conn

A DBI::DBIConnection object (from frs_db_conn()).

x

Numeric. Longitude or easting.

y

Numeric. Latitude or northing.

srid

Integer. Spatial reference ID of the input coordinates. Default 4326 (WGS84 lon/lat).

tolerance

Numeric. Maximum search distance in metres. Default 5000.

num_features

Integer. Number of candidate matches to return. Default 1.

blue_line_key

Integer. Optional. When provided, snap only to this stream. Bypasses fwa_indexpoint() and uses KNN against fwa_stream_networks_sp with measure derivation and boundary clamping.

stream_order_min

Integer. Optional. Minimum stream order for snap candidates. Ignored when blue_line_key is provided. Forces KNN path.

Value

An sf data frame with columns: linear_feature_id, gnis_name, blue_line_key, downstream_route_measure, distance_to_stream, and snapped point geom.

See also

Other index: frs_point_locate()

Examples

if (FALSE) { # \dontrun{
conn <- frs_db_conn()

# Snap to nearest stream (any)
snapped <- frs_point_snap(conn, x = -126.5, y = 54.5)

# Snap to a specific stream (Bulkley River)
snapped <- frs_point_snap(conn, x = -126.5, y = 54.5,
  blue_line_key = 360873822)

# Snap to order 4+ streams only
snapped <- frs_point_snap(conn, x = -126.5, y = 54.5, stream_order_min = 4)
DBI::dbDisconnect(conn)
} # }