osm-tools.Rdosm.ll2xy converts lat/lon coordinates to OpenStreetMap tile
numbers. osm.xy2ll performs the inverse conversion.
osm.xy2ll(x, y, zoom = 16)
osm.ll2xy(lon, lat, zoom = 16)osm.ll2xy computes tile numbers for given latitude and
longitude, osm.xy2ll does the inverse.
osm.ll2xy returns a list with the components x and y
osm.xy2ll returns a list with the components lon and lat