oce (version 1.2-0)

map2lonlat: Convert X and Y to Longitude and Latitude

Description

Convert from x-y coordinates to longitude and latitude. This is normally called internally within oce; see ‘Bugs’. A projection must already have been set up, by a call to mapPlot() or lonlat2map(). It should be noted that not all projections are handled well; see ‘Bugs’.

Usage

map2lonlat(x, y, init = NULL)

Arguments

x

vector containing the x component of points in the projected space, or a list containing items named x and y, in which case the next argument is ignored.

y

vector containing the y coordinate of points in the projected space (ignored if x is a list, as described above).

init

vector containing the initial guesses for longitude and latitude, presently ignored.

Value

A list containing longitude and latitude, with NA values indicating points that are off the globe as displayed.

Bugs

oce uses rgdal::project() in the rgdal package to handle projections. Only those projections that have inverses are permitted within oce, and even those can sometimes yield errors, owing to limitations in rgdal. On i386/windows machines, the version of rgdal must be 1.3-9 or higher, to prevent an error with map2lonlat.

See Also

lonlat2map() does the inverse operation.

A map must first have been created with mapPlot().

Other functions related to maps: formatPosition(), lonlat2map(), lonlat2utm(), mapArrows(), mapAxis(), mapContour(), mapCoordinateSystem(), mapDirectionField(), mapGrid(), mapImage(), mapLines(), mapLocator(), mapLongitudeLatitudeXY(), mapPlot(), mapPoints(), mapPolygon(), mapScalebar(), mapText(), mapTissot(), oceCRS(), shiftLongitude(), usrLonLat(), utm2lonlat()

Examples

# NOT RUN {
canProject <- .Platform$OS.type!="windows"&&requireNamespace("rgdal")
if (canProject) {
    library(oce)
    ## Cape Split, in the Minas Basin of the Bay of Fundy
    cs <- list(longitude=-64.49657, latitude=45.33462)
    xy <- lonlat2map(cs, projection="+proj=merc")
    map2lonlat(xy)
}

# }