[R-sig-Geo] spplot with two rasters

[Dylan Beaudette]

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



-- 
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341