[R-sig-Geo] spplot with two rasters

[Thomas Adams]

Dylan,

I think a solution using GRASS can be found on pages 110-11 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

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