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Obtain coordinate reference system object

Source: R/fmesher_crs.R
fm_crs.Rd

Obtain an sf::crs or fm_crs object from a spatial object, or convert crs information to construct a new sf::crs object.

Usage

fm_crs(x, ..., crsonly = FALSE)

fm_crs_oblique(x)

fm_crs_oblique(x) <- value

# S3 method for fm_crs
print(x, ...)

# S3 method for default
fm_crs(x, ..., crsonly = FALSE)

# S3 method for fm_crs
st_crs(x, ...)

# S3 method for fm_crs
$(x, name)

# S3 method for fm_crs
fm_crs(x, ..., crsonly = FALSE)

# S3 method for inla.CRS
fm_crs(x, ..., crsonly = FALSE)

# S3 method for character
fm_crs(x, ..., crsonly = FALSE)

# S3 method for Spatial
fm_crs(x, ..., crsonly = FALSE)

# S3 method for SpatVector
fm_crs(x, ..., crsonly = FALSE)

# S3 method for SpatRaster
fm_crs(x, ..., crsonly = FALSE)

# S3 method for sf
fm_crs(x, ..., crsonly = FALSE)

# S3 method for sfc
fm_crs(x, ..., crsonly = FALSE)

# S3 method for sfg
fm_crs(x, ..., crsonly = FALSE)

# S3 method for inla.mesh
fm_crs(x, ..., crsonly = FALSE)

# S3 method for inla.mesh.lattice
fm_crs(x, ..., crsonly = FALSE)

# S3 method for inla.mesh.segment
fm_crs(x, ..., crsonly = FALSE)

fm_wkt_predef()

Arguments

x

Object to convert to crs or to extract crs information from. If character, a string suitable for sf::st_crs(x), or the name of a predefined wkt string from ``names(fm_wkt_predef())`.

...

Additional parameters. Not currently in use.

crsonly

logical; if TRUE, remove any oblique information for fm_crs class objects and return a pure crs class object. Default: FALSE.

value

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.

name

element name

Value

Either an sf::crs object or an fm_crs object, depending on if the coordinate reference system described by the parameters can be expressed with a pure crs object or not.

A crs object (sf::st_crs()) or a fm_crs object. An S3 fm_crs object is a list with elements crs and oblique.

fm_wkt_predef returns a WKT2 string defining a projection

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.

Methods (by generic)

  • st_crs(fm_crs): st_crs(x, ...) is equivalent to fm_crs(x, ..., crsonly = TRUE) when x is a fm_crs object.

  • $: For a fm_crs object x, x$name calls the accessor method for the crs object inside it. If name is "crs", the internal crs object itself is returned. If name is "oblique", the internal oblique angle parameter vector is returned.

See also

sf::st_crs(), fm_crs_wkt

Author

Finn Lindgren finn.lindgren@gmail.com

Examples

crs1 <- fm_crs("longlat_globe")
crs2 <- fm_crs("lambert_globe")
crs3 <- fm_crs("mollweide_norm")
crs4 <- fm_crs("hammer_globe")
crs5 <- fm_crs("sphere")
crs6 <- fm_crs("globe")
if (FALSE) {
names(fm_wkt_predef())
}