Get precision

Get precision

Set precision attribute (without changing coordinates)

Usage

st_precision(x)

st_set_precision(x, precision)

st_precision(x) <- value

Arguments

x

object of class sfc or sf

precision

numeric, or object of class units with distance units (but see details); see st_as_binary for how to do this.

value

precision value

Details

If precision is a units object, the object on which we set precision must have a coordinate reference system with compatible distance units.

Setting a precision has no direct effect on coordinates of geometries, but merely set an attribute tag to an sfc object. The effect takes place in st_as_binary or, more precise, in the C++ function CPL_write_wkb, where simple feature geometries are being serialized to well-known-binary (WKB). This happens always when routines are called in GEOS library (geometrical operations or predicates), for writing geometries using st_write or write_sf, st_make_valid in package lwgeom; also aggregate and summarise by default union geometries, which calls a GEOS library function. Routines in these libraries receive rounded coordinates, and possibly return results based on them. st_as_binary contains an example of a roundtrip of sfc geometries through WKB, in order to see the rounding happening to R data.

The reason to support precision is that geometrical operations in GEOS or liblwgeom may work better at reduced precision. For writing data from R to external resources it is harder to think of a good reason to limiting precision.

See also

st_as_binary for an explanation of what setting precision does, and the examples therein.

Examples

x <- st_sfc(st_point(c(pi, pi)))
st_precision(x)
#> [1] 0
st_precision(x) <- 100
st_precision(x)
#> [1] 100
st_coordinates(x) # no rounding
#>             X        Y
#> [1,] 3.141593 3.141593
st_as_binary(x) |> st_as_sfc() |> st_coordinates() # rounds
#>         X    Y
#> [1,] 3.14 3.14