sf (version 1.0-14)

st_crs: Retrieve coordinate reference system from object

Description

Retrieve coordinate reference system from sf or sfc object

Set or replace retrieve coordinate reference system from object

Usage

st_crs(x, ...)
# S3 method for sf
st_crs(x, ...)
# S3 method for numeric
st_crs(x, ...)
# S3 method for character
st_crs(x, ...)
# S3 method for sfc
st_crs(x, ..., parameters = FALSE)
# S3 method for bbox
st_crs(x, ...)
# S3 method for CRS
st_crs(x, ...)
# S3 method for crs
st_crs(x, ...)
st_crs(x) <- value
# S3 method for sf
st_crs(x) <- value
# S3 method for sfc
st_crs(x) <- value
st_set_crs(x, value)
NA_crs_
# S3 method for crs
is.na(x)
# S3 method for crs
$(x, name)
# S3 method for crs
format(x, ...)
st_axis_order(authority_compliant = logical(0))

Value

If x is numeric, return crs object for EPSG:x; if x is character, return crs object for x; if x is of class sf or sfc, return its crs object.

Object of class crs, which is a list with elements input (length-1 character) and wkt (length-1 character). Elements may be NA valued; if all elements are NA the CRS is missing valued, and coordinates are assumed to relate to an arbitrary Cartesian coordinate system.

st_axis_order returns the (logical) current value if called without argument, or (invisibly) the previous value if it is being set.

Format

An object of class crs of length 2.

Arguments

x

numeric, character, or object of class sf or sfc

...

ignored

parameters

logical; FALSE by default; if TRUE return a list of coordinate reference system parameters, with named elements SemiMajor, InvFlattening, units_gdal, IsVertical, WktPretty, and Wkt

value

one of (i) character: a string accepted by GDAL, (ii) integer, a valid EPSG value (numeric), or (iii) an object of class crs.

name

element name

authority_compliant

logical; specify whether axis order should be handled compliant to the authority; if omitted, the current value is printed.

Details

The *crs functions create, get, set or replace the crs attribute of a simple feature geometry list-column. This attribute is of class crs, and is a list consisting of input (user input, e.g. "EPSG:4326" or "WGS84" or a proj4string), and wkt, an automatically generated wkt2 representation of the crs. If x is identical to the wkt2 representation, and the CRS has a name, this name is used for the input field.

Comparison of two objects of class crs uses the GDAL function OGRSpatialReference::IsSame.

In case a coordinate reference system is replaced, no transformation takes place and a warning is raised to stress this.

NA_crs_ is the crs object with missing values for input and wkt.

the $ method for crs objects retrieves named elements using the GDAL interface; named elements include "SemiMajor", "SemiMinor", "InvFlattening", "IsGeographic", "units_gdal", "IsVertical", "WktPretty", "Wkt", "Name", "proj4string", "epsg", "yx", "ud_unit", and axes (this may be subject to changes in future GDAL versions). "ud_unit" returns a valid units object or NULL if units are missing.

format.crs returns NA if the crs is missing valued, or else the name of a crs if it is different from "unknown", or else the user input if it was set, or else its "proj4string" representation;

st_axis_order can be used to get and set the axis order: TRUE indicates axes order according to the authority (e.g. EPSG:4326 defining coordinates to be latitude,longitude pairs), FALSE indicates the usual GIS (display) order (longitude,latitude). This can be useful when data are read, or have to be written, with coordinates in authority compliant order. The return value is the current state of this (FALSE, by default).

Examples

sfc = st_sfc(st_point(c(0,0)), st_point(c(1,1)))
sf = st_sf(a = 1:2, geom = sfc)
st_crs(sf) = 4326
st_geometry(sf)
sfc = st_sfc(st_point(c(0,0)), st_point(c(1,1)))
st_crs(sfc) = 4326
sfc
sfc = st_sfc(st_point(c(0,0)), st_point(c(1,1)))
sfc %>% st_set_crs(4326) %>% st_transform(3857)
st_crs("EPSG:3857")$input
st_crs(3857)$proj4string
st_crs(3857)$b     # numeric
st_crs(3857)$units # character
pt = st_sfc(st_point(c(0, 60)), crs = 4326)
# st_axis_order() only has effect in GDAL >= 2.5.0:
st_axis_order() # query default: FALSE means interpret pt as (longitude latitude)
st_transform(pt, 3857)[[1]]
old_value = FALSE
if (sf_extSoftVersion()["GDAL"] >= "2.5.0")
   (old_value = st_axis_order(TRUE))
# now interpret pt as (latitude longitude), as EPSG:4326 prescribes:
st_axis_order() # query current value
st_transform(pt, 3857)[[1]]
st_axis_order(old_value) # set back to old value