gridlines: Create N-S and E-W grid lines over a geographic region
In dis-organization/sp_dplyrexpt: Classes and Methods for Spatial Data

Description Usage Arguments Value Author(s) See Also Examples

Create N-S and E-W grid lines over a geographic region; gridat permits the construction of points and labels for non-projected grid annotation

gridlines(x, easts = pretty(bbox(x)[1,]), norths = pretty(bbox(x)[2,]),
 ndiscr = 20) 
gridat(x, easts = pretty(bbox(x)[1,]), norths = pretty(bbox(x)[2,]),
 offset=0.5, side="WS")

`x`	object deriving from class Spatial-class
`easts`	numeric; east-west values for vertical lines
`norths`	numeric; north-south values for horizontal lines
`ndiscr`	integer; number of points used to discretize the line, could be set to 2, unless the grid is (re)projected
`offset`	offset value to be returned, see text
`side`	default “WS”, if “EN” labels placed on the top and right borders

gridlines returns an object of class SpatialLines-class, with lines as specified; the return object inherits the projection information of x; gridat returns a SpatialPointsDataFrame with points at the west and south ends of the grid lines created by gridlines, with degree labels

Edzer Pebesma, edzer.pebesma@uni-muenster.de, using example code of Roger Bivand.

spTransform; llgridlines in rgdal (recent versions) for plotting long-lat grid over projected data

data(meuse)
coordinates(meuse) = ~x+y
plot(meuse)
plot(gridlines(meuse), add=TRUE)
title("default gridlines within Meuse bounding box")

if (require(rgdal)) {
proj4string(meuse) <- CRS("+init=epsg:28992")
meuse_ll <- spTransform(meuse, CRS("+proj=longlat +datum=WGS84"))
grd <- gridlines(meuse_ll)
grd_x <- spTransform(grd, CRS("+init=epsg:28992"))
plot(meuse)
plot(grd_x, add=TRUE, lty=2)
grdat_ll <- gridat(meuse_ll)
grdat_x <- spTransform(grdat_ll, CRS("+init=epsg:28992"))
text(coordinates(grdat_x), labels=parse(text=grdat_x$labels),
  pos=grdat_x$pos, offset=grdat_x$offset)
plot(meuse)
plot(grd_x, add=TRUE, lty=2)
grdat_ll <- gridat(meuse_ll, side="EN")
grdat_x <- spTransform(grdat_ll, CRS("+init=epsg:28992"))
text(coordinates(grdat_x), labels=parse(text=grdat_x$labels),
  pos=grdat_x$pos, offset=grdat_x$offset)
}