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 lonmin, lonmax,
latmin, latmax, and ok; the last
of which indicates whether at least one point on the plot box
is invertible. Note that longitude are expressed in the
range from -180 to 180 degrees.
Note: this procedure does not work for projections that have trouble
inverting points that are "off the globe". For this reason, this function
examines .Projection()$projection and if it contains the string
"wintri", then the above-stated procedure is skipped, and
the return value has each of the numerical quantities 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()