inla.CRS {INLA} | R Documentation

## Create a coordinate reference system object

### Description

Creates either a CRS object or an inla.CRS object, describing a coordinate reference system

### Usage

    inla.CRS(projargs = NA_character_, doCheckCRSArgs = TRUE,
             args = NULL, oblique = NULL, ...)

### Arguments

`projargs` | Either 1) a projection argument string suitable as input to `sp::CRS`, or 2) an existing `CRS` object, or 3) a shortcut reference string to a predefined projection (`longlat`, `lambert`, `mollweide`, `hammer`, and `sphere`).
`doCheckCRSArgs` | default TRUE, must be set to FALSE by package developers including `CRS` in an S4 class definition to avoid uncontrolable loading of the `rgdal` namespace.
`args` | An optional list of name/value pairs to add to and/or override the PROJ4 arguments in `projargs`. `name=value` is converted to `"+name=value"`, and `name=NA` is converted to `"+name"`.
`oblique` | Vector of length at most 4 of rotation angles (in degrees) for an oblique projection, all values defaulting to zero. The values indicate (longitude, latitude, orientation, orbit), as explained in the Details section below.
`...` | Additional parameters. Not currently in use.

### Details

The first two elements of the `oblique` vector are the (longitude, latitude) coordinates for the oblique centre point. The third value (orientation) is a counterclockwise rotation angle for an observer looking at the centre point from outside the sphere. The fourth value is the quasi-longitude (orbit angle) for a rotation along the oblique observers equator.

Simple oblique: `oblique=c(0, 45)`

Polar: `oblique=c(0, 90)`

Quasi-transversal: `oblique=c(0, 0, 90)`

Satellite orbit viewpoint: `oblique=c(lon0-time*v1, 0, orbitangle, orbit0+time*v2)`, where `lon0` is the longitude at which a satellite orbit crosses the equator at `time=0`, when the satellite is at an angle `orbit0` further along in its orbit. The orbital angle relative to the equatorial plane is `orbitangle`, and `v1` and `v2` are the angular velocities of the planet and the satellite, respectively. Note that "forward" from the satellite's point of view is "to the right" in the projection.

When `oblique[2]` or `oblique[3]` are non-zero, the resulting projection is only correct for perfect spheres.

### Value

Either an `sp::CRS` object or an `inla.CRS` object, depending on if the coordinate reference system described by the parameters can be expressed with a pure `sp::CRS` object or not.

An S3 `inla.CRS` object is a list, usually (but not necessarily) containing at least one element:

`crs` | The basic `sp::CRS` object

### Author(s)

Finn Lindgren <finn.lindgren@gmail.com>

### See Also

`CRS`, `inla.CRSargs`, `plot.CRS`, `inla.identical.CRS`

### Examples

    if (require(rgdal)) {
      halfroot <- "+a=0.7071067811865476 +b=0.7071067811865476"
      crs1 <- inla.CRS("+proj=longlat +ellps=sphere +a=1 +b=1")
      crs2 <- inla.CRS("+proj=cea +ellps=sphere +lat_ts=0 +units=m +a=1 +b=1")
      crs3 <- inla.CRS(paste("+proj=moll +ellps=sphere +units=m", halfroot))
      crs4 <- inla.CRS(paste("+proj=hammer +ellps=sphere +units=m", halfroot))
      crs5 <- inla.CRS("+proj=geocent +ellps=sphere +a=1 +b=1 +units=m")
      ## Shortcuts:
      crs1 <- inla.CRS("longlat")
      crs2 <- inla.CRS("lambert")
      crs3 <- inla.CRS("mollweide")
      crs4 <- inla.CRS("hammer")
      crs5 <- inla.CRS("sphere")
    }

[Package INLA version 18.07.12 Index]