fm_crs: Obtain coordinate reference system object

In fmesher: Triangle Meshes and Related Geometry Tools

Obtain coordinate reference system object

Description

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, ..., units = NULL, oblique = NULL)

fm_crs_oblique(x)

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

## S3 method for class 'fm_crs'
x$name

## Default S3 method:
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'crs'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'fm_crs'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'fm_CRS'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'character'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'Spatial'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'SpatVector'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'SpatRaster'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'sf'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'sfc'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'sfg'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'fm_mesh_2d'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'fm_mesh_1d'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'fm_mesh_3d'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'fm_tensor'
fm_crs(x, ..., units = NULL, oblique = NULL, .multi = FALSE)

## S3 method for class 'fm_collect'
fm_crs(x, ..., units = NULL, oblique = NULL, .multi = FALSE)

## S3 method for class 'fm_lattice_2d'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'fm_segm'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'fm_list'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'matrix'
fm_crs(x, ..., units = NULL, oblique = NULL)

## S3 method for class 'fm_list'
fm_CRS(x, ..., units = NULL, oblique = NULL)

fm_wkt_predef()

## S3 method for class 'inla.CRS'
fm_crs(x, ..., units = NULL, oblique = NULL)

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.
units	character; if non-NULL, ⁠fm_length_unit()<-⁠ is called to change the length units of the crs object. If NULL (default), the length units are not changed. (From version ⁠0.3.0.9013⁠)
oblique	Numeric 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. When oblique is non-NULL, used to override the obliqueness parameters of a fm_crs object. When NA, remove obliqueness from the object, resulting in a return class of sf::st_crs(). When NULL, pass though any oblique information in the object, returning an fm_crs() object if needed.
name	element name
.multi	logical; If TRUE, return a list of fm_crs objects for classes that support multiple spaces. Default FALSE

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 counter-clockwise 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 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

Methods (by class)

• fm_crs(fm_tensor): By default returns the crs of the first space in the tensor product space.

• fm_crs(fm_collect): By default returns the crs of the first space in the collection.

• fm_crs(fm_list): returns a list of 'crs' objects, one for each list element

Methods (by generic)

• st_crs(fm_crs): st_crs(x, ...) is equivalent to fm_crs(x, oblique = NA, ...) 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.

Functions

• fm_crs_oblique(): Return NA for object with no oblique information, and otherwise a length 4 numeric vector.

• fm_CRS(fm_list): returns a list of 'CRS' objects, one for each list element

Author(s)

Finn Lindgren [e-mail]

See Also

sf::st_crs(), fm_crs_wkt

fm_crs_is_null

fm_crs<-(), fm_crs_oblique<-()

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")
names(fm_wkt_predef())

fmesher documentation built on Aug. 9, 2025, 1:10 a.m.