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Find Nearby SMN Stations and/or NASA Grid Nodes (Hybrid)

Source: R/tl_find_nearby.R
smn_tl_find_nearby.Rd

Given a reference point (station code or coordinates), return nearby nodes from the SMN station catalog and/or a prebuilt NASA-like grid (e.g. 1-km DEM grid) with great-circle distances. Two selection modes are supported:

  • mode = "radius": all nodes within radius_km

  • mode = "k": the k nearest nodes

Usage

smn_tl_find_nearby(
  station = NULL,
  lat = NULL,
  lon = NULL,
  sources = c("both", "smn", "nasa"),
  mode = c("radius", "k"),
  radius_km = 20,
  k = 10,
  bbox_pad_km = 2
)

Arguments

station

Optional. SMN station code to use as reference point.

lat, lon

Optional numeric coordinates (decimal degrees WGS84) for the reference point. If station is not supplied, both lat and lon must be provided.

sources

Character vector: "smn", "nasa" or "both" (default). Controls which catalogs are queried.

mode

Selection mode: "radius" (default) or "k".

radius_km

Numeric radius in kilometers (used when mode="radius"). Default 20.

k

Integer number of nearest neighbors (used when mode="k"). Default 10.

bbox_pad_km

Numeric padding (km) for a quick prefiltering bounding box before exact distances (speeds up large catalogs). Default 2 km.

Value

A data frame with rows for the nearby nodes and columns: source (factor: "SMN" or "NASA_POWER"), station (character ID; for grid is the numeric node code), latitude, longitude, altitude, distance_km (great-circle distance to the reference point). Rows are ordered by distance_km.

Details

The function expects two datasets bundled in the package (or preloaded):

  • stations: SMN catalog with columns station, latitude, longitude, altitude (altitude may be NA)

  • gridmex: Grid of candidate nodes with columns station, latitude, longitude, altitude

The great-circle distance is computed with the haversine formula via geosphere. A coarse degree bounding box (radius_km + bbox_pad_km)/111 is applied first for speed.

If station (reference) is supplied, its coordinates are taken from stations. If not found, an error is raised unless lat/lon are provided.

Examples

if (FALSE) { # \dontrun{
# 1) 20 km around station 15101, combining SMN + Grid
smn_tl_find_nearby(station = "15101", mode = "radius", radius_km = 20)

# 2) 15 vecinos más cercanos solo del grid, a coordenadas dadas
smn_tl_find_nearby(lat = 19.29, lon = -99.66, sources = "nasa",
                   mode = "k", k = 15)
} # }