Add graticule to map using levelplot R - r

Question

Often there is the need to produce stylish maps for inclusion in publications.
How can one possibly include projected grid coordinates in a map generated preferably with levelplotto look like those in the map shown here:
I provide sample data (for Canada) below for reproducibility. A typical projcetion for Canada is dat = projectRaster(dem, crs = ('+proj=stere +lat_0=90 +lat_ts=60 +lon_0=-110 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs')) and SpTransform can be used to tranform the boundary lines (can1).
require(colorRamps)
require(raster)
require(rasterVis)
require(mapproj)
library(raster)
library(proj4)
# Get province borders and project it to same CRS than raster
can1 <- getData('GADM', country="CAN", level=1)
getData('ISO3') # country name
dem=getData('alt', country='CAN', mask=TRUE)
require( colorRamps )
my.at <- unique(round(seq(ceiling(5800), floor(1), length.out = 51),0))#at: numeric vector specifying where the colors change. must be of length 1 more than the col vector.
col<-colorRampPalette(c("#d9d9d9", "#bdbdbd", "#969696", "#737373", "#525252", "#252525", "#000000"))
levelplot(dem,maxpixel=ncell(dem),panel=panel.levelplot.raster,names.attr=names(dem),
interpolate=F,margin=FALSE,xlab=list(label="Longitude",cex=1.5),yscale.components = yscale.raster.subticks,
xscale.components = xscale.raster.subticks,
ylab=list(label="Latitude",cex=1.5),
par.strip.text=list(cex=1),xlim=c(-158, -48.99485),
ylim=c(38.00513, 85),col.regions=col,at = seq(0, 5800,100),
colorkey = list(space = "bottom", labels = list(at = seq(0, 5800,800), rot=0,cex=1.1,font=6,fontface=1,
labels =c("0", "800", "1600", "2400", "3200", "4000", "4800", "5600")),
height=0.99,width=1.8,tck = c(0,0)),
par.settings=list(panel.background=list(col="white"),axis.line=list(lwd=1.9), strip.border=list(lwd=1.9),layout.heights=list(xlab.key.padding=-0.2)),
cex=0.8, scales = list(x=list(draw=TRUE,cex=1.2), y=list(draw=TRUE,cex=1.2)))+
layer(sp.polygons(can1,lwd=0.5,col="gray40"))

Answer 1

Next code provides a solution using the graticule package:
library(raster)
library(rasterVis)
library(graticule)
r <- getData('alt', country='CAN', mask=TRUE)
## Here is where the graticule routine starts
crs.longlat <- CRS("+init=epsg:4326")
prj <- CRS(projection(r))
extLL <- projectExtent(r, crs = crs.longlat)
lons <- pretty(c(xmin(extLL), xmax(extLL)))
lats <- pretty(c(ymin(extLL), ymax(extLL)))
## optionally, specify the extents of the meridians and parallels
## here we push them out a little on each side
xl <- range(lons) + c(-0.4, 0.4)
yl <- range(lats) + c(-0.4, 0.4)
## build the lines with our precise locations and ranges
grat <- graticule(lons, lats, proj = prj,
xlim = xl, ylim = yl)
## Labels
labs <- graticule_labels(lons, lats,
xline = lons[2],
yline = lats[2],
proj = prj)
labsLon <- labs[labs$islon,]
labsLat <- labs[!labs$islon,]
## Display the raster
levelplot(r) +
## and the graticule
layer(sp.lines(grat)) +
layer(sp.text(coordinates(labsLon),
txt = parse(text = labsLon$lab),
adj = c(1.1, -0.25),
cex = 0.6)) +
layer(sp.text(coordinates(labsLat),
txt = parse(text = labsLat$lab),
adj = c(-0.25, -0.25),
cex = 0.6))