Add a Longitude and Latitude Grid to a Map

Description

Plot longitude and latitude grid on an existing map.

Usage

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mapGrid(dlongitude = 15, dlatitude = 15, longitude, latitude,
  col = "darkgray", lty = "solid", lwd = 0.5 * par("lwd"),
  polarCircle = 0, longitudelim, latitudelim, debug = getOption("oceDebug"))

Arguments

dlongitude

increment in longitude, ignored if longitude is supplied, but otherwise determines the longitude sequence.

dlatitude

increment in latitude, ignored if latitude is supplied, but otherwise determines the latitude sequence.

longitude

vector of longitudes, or NULL to prevent drawing longitude lines.

latitude

vector of latitudes, or NULL to prevent drawing latitude lines.

col

colour of lines

lty

line type

lwd

line width

polarCircle

a number indicating the number of degrees of latitude extending from the poles, within which zones are not drawn.

longitudelim

optional argument specifying suggested longitude limits for the grid. If this is not supplied, grid lines are drawn for the whole globe, which can yield excessively slow drawing speeds for small-region plots. This, and latitudelim, are both set by mapPlot if the arguments of the same name are passed to that function.

latitudelim

similar to longitudelim.

debug

a flag that turns on debugging. Set to 1 to get a moderate amount of debugging information, or to 2 to get more.

Details

This is somewhat analogous to grid, except that the first two arguments of the latter supply the number of lines in the grid, whereas the present function has increments for the first two arguments.

Plans

At the moment, the function cannot determine which lines might work with labels on axes, but this could perhaps be added later, making this more analogous with grid.

Author(s)

Dan Kelley

See Also

A map must first have been created with mapPlot.

Other functions related to maps: lonlat2map, lonlat2utm, map2lonlat, mapArrows, mapAxis, mapContour, mapDirectionField, mapImage, mapLines, mapLocator, mapLongitudeLatitudeXY, mapPlot, mapPoints, mapPolygon, mapScalebar, mapText, mapTissot, oceCRS, shiftLongitude, utm2lonlat

Examples

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## Not run: 
library(oce)
data(coastlineWorld)
mapPlot(coastlineWorld, type='l', grid=FALSE,
longitudelim=c(-80,10), latitudelim=c(0,120),
projection="+proj=ortho")
mapGrid(15, 15, polarCircle=15)

## End(Not run)

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