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: lonlat2map,
lonlat2utm, map2lonlat,
mapArrows, mapAxis,
mapContour,
mapDirectionField, mapGrid,
mapImage, mapLines,
mapLocator,
mapLongitudeLatitudeXY,
mapPlot, mapPoints,
mapPolygon, mapScalebar,
mapText, mapTissot,
oceCRS, shiftLongitude,
utm2lonlat