Get precision

Set precision

```
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) <- 0.01
st_precision(x)
#> [1] 0.01
```