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 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 >>> > > > > -- Thomas E Adams National Weather Service Ohio River Forecast Center 1901 South State Route 134 Wilmington, OH 45177 EMAIL: [EMAIL PROTECTED] VOICE: 937-383-0528 FAX: 937-383-0033 _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo