[R-sig-Geo] using spplot to superimpose points and polygons on SpatialGridDataFrame

[Roger Bivand]

On Sun, 23 Sep 2007, reeves at nceas.ucsb.edu wrote:

>
>
> Hello:
>
> Thanks to the excellent example at:
>
> http://casoilresource.lawr.ucdavis.edu/drupal/node/442
>
> I am close to my goal of creating a map diagram in R
> using raster and vector data layers.
>
> I have set up a similar diagram using as inputs a satellite image
> and point shapefile:
>
>  cPts = readShapePoints("PSCentroidPointShape")
>  ProjString = proj4string(MapPolysDataFrame)
>  proj4string(cPts) = CRS(ProjString)
>  psImg = readGDAL("PugetSoundSub1.img")
> #
> # psImg is a SpatialGridDataFrame
> #
>  image(PsImg) # just display the raster
> #
> # one way to superimpose vectors over rasters
> #
>  ctysPS = SpatialPolygons2PolySet(ctys)
>  points(cPts,add=TRUE)
>  addPolys(ctysPS)

Unless you need to go to PolySets, you could say plot(ctys, add=TRUE).

> #
> # now, see if spplot works as indicated in this case by overlaying
> # the points over the grid.
> #
>  points <- list("sp.points", cPts, pch = 4, col = "black", cex=0.5)
>  greys= grey(0:256 / 256)
> #
>  spplot(psImg,zcol="band1",col.regions=greys,main="my
> Plot",sp.layout=list(points))
>
> OK, This generates a diagram, but the points are drawn FIRST, not
> second, so they are not visible on top of the image.
>

With:

library(sp)
data(meuse)
data(meuse.grid)
coordinates(meuse) <- c("x", "y")
coordinates(meuse.grid) <- c("x", "y")
gridded(meuse.grid) <- TRUE
pts <- list("sp.points", meuse, pch = 4, col = "black", cex=0.5)
greys <- grey(0:256 / 256)
spplot(meuse.grid, "dist", col.regions=greys, sp.layout=list(pts))

though you need to match the # cuts to the col.regions:

spplot(meuse.grid, "dist", col.regions=greys, sp.layout=list(pts),
   cuts=length(greys)-1)

I cannot reproduce your problem. Could you try to demonstrate it with the 
provided data set, so that we can try to isolate the issue?

Roger


> This conflicts the Web site example, and the spplot help file:
>
> The order of items in sp.layout matters; objects are drawn in the order
> they appear. Plot order and prevalence of sp.layout items: for points and
> lines,
> sp.layout items are drawn before the points (to allow for grids and
> polygons);
>
> ** for grids and polygons sp.layout is drawn afterwards (so the item will
> not be overdrawn by the grid and/or polygon). **
>
> Although a matter of taste, transparency may help when combining things.
>
> The only difference that I can see between my attempt and the web site
> example is that the example uses a SpatialPixelsDataFrame as a base layer.
>
> Can anyone offer insight?
>
>
> And a side question: Is there a way to eliminate the grey level scale on
> the right side of the spplot-generated diagram?
>
> Version of R used: R version 2.5.0 (2007-04-23) (and also version 2.5.1)
>
> I can provide the data files if necessary.
>
> Thanks, Rick R
>
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>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no