gridlines {sp} | R Documentation |
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) }