sp (version 1.2-0)

CRS-class: Class "CRS" of coordinate reference system arguments

Description

Interface class to the PROJ.4 projection system. The class is defined as an empty stub accepting value NA in the sp package. If the rgdal package is available, then the class will permit spatial data to be associated with coordinate reference systems. The arguments must be entered exactly as in the PROJ.4 documentation, in particular there cannot be any white space in += strings, and successive such strings can only be separated by blanks. Note that only +proj=longlat +ellps=WGS84 is accepted for geographical coordinates, which must be ordered (eastings, northings); the +ellps= definition must be given (or expanded internally from a given +datum= value) for recent versions of the PROJ.4 library, and should be set to an appropriate value.

Usage

CRS(projargs)
identicalCRS(x,y)

Arguments

projargs

A character string of projection arguments; the arguments must be entered exactly as in the PROJ.4 documentation; if the projection is unknown, use as.character(NA), it may be missing or an empty string of zero length and will then set to the

x

object having a proj4string method, or if y is missing, list with objects that have a proj4string method

y

object of class Spatial, or having a proj4string method

Value

• CRS returns on success an object of class CRS. identicalCRS returns a logical, indicating whether x and y have identical CRS, or if y is missing whether all objects in list x have identical CRS.

Objects from the Class

Objects can be created by calls of the form CRS("projargs"), where "projargs" is a valid string of PROJ.4 arguments. The initiation function calls the PROJ.4 library to verify the argument set against those known in the library, returning error messages where necessary. The function CRSargs() can be used to show the expanded argument list used by the PROJ.4 library.

References

https://github.com/OSGeo/proj.4

Examples

CRS()
CRS("")
CRS(as.character(NA))
CRS("+proj=longlat +datum=WGS84")
if (require(rgdal)) {
  print(CRSargs(CRS("+proj=longlat +datum=NAD27")))
  print(CRSargs(CRS("+init=epsg:4267")))
  print(CRSargs(CRS("+init=epsg:26978")))
  print(CRSargs(CRS(paste("+proj=sterea +lat_0=52.15616055555555",
 "+lon_0=5.38763888888889 +k=0.999908 +x_0=155000 +y_0=463000 +ellps=bessel",
 "+towgs84=565.237,50.0087,465.658,-0.406857,0.350733,-1.87035,4.0812 +units=m"))))
  print(CRSargs(CRS("+init=epsg:28992")))
}
# see http://trac.osgeo.org/gdal/ticket/1987