RMtrafo: Transformation of coordinate systems
In RandomFields: Simulation and Analysis of Random Fields

Description Usage Arguments Details Value Note References See Also Examples

The functions transform a coordinate system into another coordinate system. Currently, essentially only from the earth system to cartesian.

RMtrafo is the internal basic function that also allows to reduce vectors to their norm.

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RMtrafo(phi, new)
RFearth2cartesian(coord, units=NULL, system="cartesian", grid=FALSE)
RFearth2dist(coord, units=NULL, system="cartesian", grid=FALSE, ...)

`new`	integer or character. One of the values `RC_ISOTROPIC`, `RC_SPACEISOTROPIC`, `RC_CARTESIAN_COORD`, `RC_GNOMONIC_PROJ`, `RC_ORTHOGRAPHIC_PROJ` or the corresponding `RC_ISONAMES`. Note that `RMtrafo` only allows for integer values. Default: `RC_CARTESIAN_COORD`.
`phi`	optional submodel
`coord`	matrix or vector of earth coordinates
`units`	"km" or "miles"; if not given and `RFoptions()$general$units != ""`, the latter is used. Otherwise `"km"`.
`system`	integer or character. The coordinate system, e.g. `"cartesian"`, `"gnomonic"` or `"orthographic"`.
`grid`	logical. Whether the given coordinates are considered to be on a grid given by `c(start, step, length)`. Default: `FALSE`.
`...`	the optional arguments of `dist`

The functions transform between different coordinate systems.

The function RMtrafo returns a matrix, in general. For fixed column, the results, applied to each row of the matrix, are returned.

The function RFearth2cartesian returns a matrix in one-to-one correspondence with coord assuming that the earth is an ellipsoid.

The function RFearth2dist calculates distances, cf. dist, assuming that the earth is an ellipsoid.

Important options are units and coordinate_system, see RFoptions.

Note also that the zenit must be given explicitly for projection onto a plane. See the examples below.

For calculating the earth coordinates as ellipsoid:

constants, RMangle, RMid, RMidmodel.

data(weather)
(coord <- weather[1:5, 3:4])

(z <- RFfctn(RMtrafo(new=RC_CARTESIAN_COORD), coord))
(z1 <- RFearth2cartesian(coord)) ## equals z
z1 - z ## 0, i.e., z1 and t(z) are the same
dist(z)


(d <- RFearth2dist(coord)) 
d - dist(z) ## 0, i.e., d and dist(z) are the same


## projection onto planes
RFoptions(zenit=c(-122,   47))
RFearth2cartesian(coord, system="gnomonic")
RFearth2cartesian(coord, system="orthographic")