mapLongitudeLatitudeXY: Convert from longitude and latitude to x and y
Description
Find (x,y) values corresponding to (longitude, latitude) values,
using the present projection.
Usage
mapLongitudeLatitudeXY(longitude, latitude)
Arguments
longitude
longitudes of points, or an object from which latitude and
longitude can be inferred (e.g. a coastline file, or the return value
from mapLocator), in which case the following two
latitude
latitudes of points, needed only if they cannot be inferred
from from the first argument