spplot with two rasters

Agus, I disagree with your claim that R plot functions are not ok for
real applications. Also, I use real applications for learning and
teaching -- they are not fundamentally different.

In the trellis panel functions, or in the direct plot/image/lines etc
functions, you plot in data coordinates. The main thing that the plot
and spplot methods in package sp control is the aspect ratio. How else
do data coordinates differ from geographical coordinates when it comes
to plotting?

Are you refering to taking care of geographic (re)projection at that level?
--
Edzer

Agustin Lobo wrote:

Well, the problem is that R does not have a real geographical
display. While things can be done going back and forth from R to GIS,
this procedure soon becomes very inconvenient. It's ok
for learning and teaching, but not for real applications.
Maybe getting an existing GIS to display spatial R objects
is actually easier than developing a geographical display for R.
Agus

Dylan Beaudette escribi?:

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.

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