Trace along the plot box, converting from xy coordinates to lonlat
coordinates. The results are used by mapGrid()
and mapAxis() to ignore out-of-frame grid
lines and axis labels.
usrLonLat(n = 25, debug = getOption("oceDebug"))number of points to check along each side of the plot box
an integer specifying whether debugging information is
to be printed during the processing. This is a general parameter that
is used by many oce functions. Generally, setting debug=0
turns off the printing, while higher values suggest that more information
be printed. If one function calls another, it usually reduces the value of
debug first, so that a user can often obtain deeper debugging
by specifying higher debug values.
A list containing numerical
values lonmin, lonmax, latmin, and latmax, along
with logical value ok. The last of these indicates
whether at least one point on the plot box is invertible.
Note that longitudes are in the range from -180 to 180 degrees.
Some projections, such as "wintri", have trouble inverting
points that are "off the globe". In such cases,
the returned value has lonmin, lonmax, latmin and
latmax set to NA, and ok set to FALSE.
Other functions related to maps:
formatPosition(),
lonlat2map(),
lonlat2utm(),
map2lonlat(),
mapArrows(),
mapAxis(),
mapContour(),
mapCoordinateSystem(),
mapDirectionField(),
mapGrid(),
mapImage(),
mapLines(),
mapLocator(),
mapLongitudeLatitudeXY(),
mapPlot(),
mapPoints(),
mapPolygon(),
mapScalebar(),
mapText(),
mapTissot(),
oceCRS(),
shiftLongitude(),
utm2lonlat()