Harmonize CRS between two spatial objects

Aligns two sf objects to a common CRS.

Usage

harmonize_crs(
  a,
  b,
  prefer = c("a", "b"),
  target_crs = NULL,
  on_transform_error = c("stop", "set_crs")
)

Arguments

a, b

Objects of class sf or sfc.

prefer

Which object's CRS to keep ("a" or "b").

target_crs

Optional target CRS to apply to both: anything sf::st_crs() accepts, including an sf or sfc object, whose CRS is used.

on_transform_error

What to do when st_transform() fails: "stop" (default) raises an error immediately; "set_crs" falls back to st_set_crs() (UNSAFE: coordinates are NOT reprojected, only the CRS label is overwritten). The "set_crs" option exists only for rare edge cases where you are certain the coordinates already match the target CRS definition.

Value

A named list with components a and b.

Details

When one input carries no CRS, the same lon/lat heuristic ensure_projected() uses decides what happens, so both entry points place identical data in the same place: coordinates that look like degrees are taken as EPSG:4326 and reprojected to the other object's CRS (or target_crs); coordinates that do not are stamped with sf::st_set_crs(), which relabels without moving them. Either way the assumption is announced with a warning.

See also

Other spatial data preparation: clip_target_for(), coerce_to_points(), ensure_projected(), prep_model_data()

Examples

library(sf)
a <- st_as_sf(data.frame(x = c(500000, 500100), y = c(4000000, 4000100)),
              coords = c("x", "y"), crs = 32632)
b <- st_transform(a, 4326)                 # same points, lon/lat
h <- harmonize_crs(a, b)                    # b is brought into a's CRS
c(a = st_crs(h$a)$epsg, b = st_crs(h$b)$epsg)
#>     a     b 
#> 32632 32632 
st_crs(h$a) == st_crs(h$b)
#> [1] TRUE