spplot with two rasters

On Wed, 12 Mar 2008, Dylan Beaudette wrote:

On Thursday 06 March 2008, Thomas Adams wrote:

Dylan,

I think a solution using GRASS can be found on pages 110-111 of "Open
Source GIS: A GRASS GIS Approach", 3rd Ed. The same material is covered
in the 2nd Ed. as well, where you use r.mapcalc to combine two rasters
and judicious use of MASKs; a conditional statement in r.mapcalc is the
key.

Regards,
Tom

Hi Tom,

Thanks for the suggestion. This works, but we were hoping to make the
plot in R-- as the PDF output is hard to match with GRASS alone. I
suppose I will just have to try using two rasters with spplot() and see
what happens.

The problem is that customising a panel to insert an image probably means
writing just that, customised panels, and spplot() essentially does that
already. You could look at Chapter 5 in Paul Murrell's book, to see how to
insert grid output into lattice output (to try to put an image as a
backcloth, but there is no example for this case - the example is for
adding a location position.

My guess would be that if you are only displaying a single panel, you will
find it easier to use base graphics, and simply say image() twice, and use
legend() (or legend.krige() from geoR).

Roger

Cheers,

Dylan

Dylan Beaudette wrote:

On Tuesday 04 March 2008, Edzer Pebesma wrote:

I find it hard to imagine how you want to plot two raster files on top
of each other. Do you want some form of transparency? If it is just
one overlaying the other, you could use overlay to find out which
cells in raster 1 to replace with those in raster 2 before plotting.
--
Edzer

Hi Edzer,

I generally agree that plotting one raster file "over" another raster
file would be of little use. In this case, one of the raster files (the
interesting one) has been masked with nodata, such that it only really
covers about 30% of the region of interest. The other raster is just
contextual data, and thus would be useful to plot "behind" the first
raster.

Ideas?

Dylan

Dylan Beaudette wrote:

Hi,

Is it possible to plot two raster images using spplot() in a manner
similar to:

pts <- list("sp.points", points_file, pch = 4, col = "black",
cex=0.5) spplot(raster_file, zcol="elev.pred", sp.layout=list(pts))

Note that one of the raster images is an aerial photo, used only for
context, while the second one is one with interesting z-values. The
second raster is masked and thus does not cover the entire region.

Thanks,

Dylan