[R-sig-Geo] spplot with two rasters

[Roger Bivand]

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
>
>
>
>

-- 
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