FAQs
Table of Contents
- How to define the breaks
- How to suppress axis labels and ticks
- How to rotate the axis label or use a different color
- How to add an arrow
- How to add an scale
- How to overlay a shapefile
- How to overlay graticules (longitude - latitude lines)
- How to print several Rasters with different legends in the same page
- How to label each panel with a different label from the layer name
How to define the breaks
Use the at argument to define the breaks.
f <- system.file("external/test.grd", package="raster")
r <- raster(f)
my.at <- seq(100, 1850, by = 250)
levelplot(r, at=my.at)
Moreover, if you want to define where the labels are located
define the components of colorkey:
myColorkey <- list(at=my.at, ## where the colors change
labels=list(
at=my.at ## where to print labels
))
levelplot(r, at=my.at, colorkey=myColorkey)
Last, you can even define the contents of the labels:
myColorkey <- list(at=my.at, ## where the colors change
labels=list(
labels=letters[seq_along(my.at)], ## labels
at=my.at ## where to print labels
))
levelplot(r, at=my.at, colorkey=myColorkey)
How to suppress axis labels and ticks
Use xlab=NULL, ylab=NULL and draw=FALSE inside scale.
r <- raster()
r <- init(r, runif)
levelplot(r, xlab=NULL, ylab=NULL, scales=list(draw=FALSE))
levelplot(r, xlab=NULL, scales=list(x=list(draw=FALSE)))
levelplot(r, ylab=NULL, scales=list(y=list(draw=FALSE)))
How to rotate the axis label or use a different color
Define main, xlab and ylab as vectors or lists with
arguments to be passed to grid::gpar.
r <- raster(nrow=10, ncol=10)
r[] <- runif(100)
levelplot(r, margin=FALSE,
main=list('My plot', col='red'),
xlab=c('Longitude', 'X-Axis'),
ylab=list('Latitude', rot=30, fontface='bold')
)
How to add an arrow
Use sp::layout.north.arrow with latticeExtra::layer.
f <- system.file("external/test.grd", package="raster")
r <- raster(f)
levelplot(r, margin=FALSE, auto.key=FALSE, scales=list(draw=FALSE)) +
layer({
SpatialPolygonsRescale(layout.north.arrow(),
offset = c(179000,332500),
scale = 400)
})
How to add an scale
Use grid.rect, grid.text and latticeExtra::layer.
f <- system.file("external/test.grd", package="raster")
r <- raster(f)
levelplot(r) +
layer({
xs <- seq(181000, 181400, by=100)
grid.rect(x=xs, y=330500,
width=100, height=30,
gp=gpar(fill=rep(c('transparent', 'black'), 2)),
default.units='native')
grid.text(x= xs - 50, y=330560, seq(0, 400, by=100),
gp=gpar(cex=0.5), rot=30,
default.units='native')
})
How to overlay a shapefile
Several layers can be combined using the +.trellis and layer
functions from the latticeExtra package (which is automatically
loaded with rasterVis).
Let’s build some data to play. You can skip this part if you already have a raster file and a shapefile.
library(maps)
library(mapdata)
library(maptools)
## raster
myRaster <- raster(xmn=-100, xmx=100, ymn=-60, ymx=60)
myRaster <- init(myRaster, runif)
## polygon shapefile
ext <- as.vector(extent(myRaster))
boundaries <- map('worldHires', fill=TRUE,
xlim=ext[1:2], ylim=ext[3:4],
plot=FALSE)
## read the map2SpatialPolygons help page for details
IDs <- sapply(strsplit(boundaries$names, ":"), function(x) x[1])
bPols <- map2SpatialPolygons(boundaries, IDs=IDs,
proj4string=CRS(projection(myRaster)))
The polygons are printed with sp::sp.polygons using +.trellis and
layer to display them over the result of levelplot.
levelplot(myRaster) + layer(sp.polygons(bPols))
Read the help page of sp.polygons for detailed information about its
options.
How to overlay graticules (longitude - latitude lines)
How to print several Rasters with different legends in the same page
Use print.trellis and its argument split.
For two different RasterLayer.
r <- r2 <- raster()
r[] <- runif(ncell(r))
r2[] <- 1:10
p <- levelplot(r, par.settings=RdBuTheme(), margin=FALSE)
p2 <- levelplot(r2, par.settings=BTCTheme(), margin=FALSE)
print(p, split=c(1, 1, 1, 2), more=TRUE)
print(p2, split=c(1, 2, 1, 2))
A more sophisticated solution to print more than two layers.
s <- stack(r, r2, 10*r+r2, 10*r-r2)
nl <- nlayers(s)
m <- matrix(1:nl, nrow=2)
themes <- list(RdBuTheme(), BTCTheme(), GrTheme(), PuOrTheme())
for (i in 1:nl){
p <- levelplot(s, layers=i,
par.settings=themes[[i]],
margin=FALSE)
print(p, split=c(col(m)[i], row(m)[i], ncol(m), nrow(m)), more=(i<nl))
}
