Return distances to nearest known locations — table_getNearestDistance • MazamaLocationUtils

Returns distances between target locations and the closest location found in locationTbl (if any). Target locations are specified with longitude and latitude.

For each target location, only a single distance to the closest known location is returned. If no known location is found within distanceThreshold, the distance associated with that target location will be NA. The length and order of resulting distances will match the order of the incoming target locations.

table_getNearestDistance(
  locationTbl = NULL,
  longitude = NULL,
  latitude = NULL,
  distanceThreshold = NULL,
  measure = c("geodesic", "haversine", "vincenty", "cheap")
)

Arguments

locationTbl: Tibble of known locations.
longitude: Vector of target longitudes in decimal degrees E.
latitude: Vector of target latitudes in decimal degrees N.
distanceThreshold: Distance in meters.
measure: One of "geodesic", "haversine", "vincenty" or "cheap" specifying desired method of geodesic distance calculation.

Value

Vector of closest distances between target locations and known locations.

Note

The measure "cheap" may be used to speed things up depending on the spatial scale being considered. Distances calculated with measure = "cheap" will vary by a few meters compared with those calculated using measure = "geodesic".

See geodist for details.

Use Case

You may have a set of locations of interest for which you want to assess whether any monitoring locations are nearby. In this case, the locations of interest will provide longitude and latitude while locationTbl will be the known location table associated with the monitoring locations.

The resulting vector of distances will tell you the distance, for each target location, to the nearst monitoring location.

Examples

library(MazamaLocationUtils)

locationTbl <- get(data("wa_monitors_500"))

# Wenatchee
lon <- -120.325278
lat <- 47.423333

# Too small a distanceThreshold will not find a match
table_getNearestDistance(locationTbl, lon, lat, distanceThreshold = 50)
#> [1] NA

# Expanding the distanceThreshold will find one
table_getNearestDistance(locationTbl, lon, lat, distanceThreshold = 5000)
#> [1] 1495.593