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Lookup time zones of sf or sp points

Source: R/tz_lookup.R
tz_lookup.Rd

There are two methods - "fast", and "accurate". The "fast" version can look up many thousands of points very quickly, however when a point is near a time zone boundary and not near a populated centre, it may return the incorrect time zone. If accuracy is more important than speed, use method = "accurate".

Usage

tz_lookup(x, crs = NULL, method = "fast", warn = TRUE)

Arguments

x

either an sfc or sf points or SpatialPoints(DataFrame) object

crs

the coordinate reference system: integer with the EPSG code, or character with proj4string. If not specified (i.e., NULL) and x has no existing crs, EPSG: 4326 is assumed (lat/long).

method

method by which to do the lookup. Either "fast" (default) or "accurate".

warn

By default, if method = "fast" a warning is issued about the potential for inaccurate results. Set warn to FALSE to turn this off.

Value

character vector the same length as x specifying the time zone of the points.

Details

Note that there are some regions in the world where a single point can land in two different overlapping time zones. The "accurate" method includes these, and when they are encountered they are concatenated in a single string, separated by a semicolon. The data used in the "fast" method does not include overlapping time zones at this time.

Examples

if (require("sf")) {

state_pts <- lapply(seq_along(state.center$x), function(i) {
  st_point(c(state.center$x[i], state.center$y[i]))
})

state_centers_sf <- st_sf(st_sfc(state_pts))

state_centers_sf$tz <- tz_lookup(state_centers_sf)

plot(state_centers_sf[, "tz"])
}
#> Loading required package: sf
#> Linking to GEOS 3.10.2, GDAL 3.4.1, PROJ 8.2.1; sf_use_s2() is TRUE
#> Warning: Using 'fast' method. This can cause inaccuracies in time zones
#>   near boundaries away from populated ares. Use the 'accurate'
#>   method if accuracy is more important than speed.