Combining different rasters

Dear list,

I have two rasters ?with different origins, resolutions and extents. Raster 2 covers a sub-area of raster 1, which has a larger resolution and larger extent than raster 2. How can I change raster 2 so that every cell in raster 2 corresponds to another cell in raster 1 ? I have looked at different functions like mosaic() and overlay() but those functions do not seem to be applicable.

Thank you very much for any suggestions.

Juliane




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Or better still, provide a self contained example as below:

r1 <- raster(ncol=25, nrow=25, xmn=-50, xmx=50, ymn=-50, ymx=50)
r2 <- raster(ncol=25, nrow=25, xmn=-3.5, xmx=20, ymn=-3.5, ymx=20)
r1[] ?<- 1:ncell(r1)
r2[] ?<- 1:ncell(r2)
plot(r1)
plot(rasterToPolygons(r2), add=T)

# one approach
x <- resample(r1, r2, method='bilinear')

# what you asked for:
# first aggregate to apprixmately the same resolution
y <- aggregate(r2, floor(res(r1) / res(r2)), fun=mean)
# then resample
z <- resample(y, r1, method='bilinear')
plot(r1)
plot(rasterToPolygons(z), add=T)



On Mon, Sep 19, 2011 at 2:19 PM, steven mosher <moshersteven at gmail.com>
wrote:

?Hi Dr. Struve,

?could you print out the characteristics of your rasters.

?Just type the name of the raster at the console and cut and paste the
output ?in a mail.
?I think your first step is probably going to be getting them in the
same resolution..
?Then match up the extents by cropping the larger one.. ?But if you
show the details It will probably help folks give you a more direct
answer..

On Mon, Sep 19, 2011 at 2:13 PM, Struve,Juliane <jstruve at ufl.edu> wrote:

Dear list,

I have two rasters ?with different origins, resolutions and extents.
Raster 2 covers a sub-area of raster 1, which has a larger resolution and
larger extent than raster 2. How can I change raster 2 so that every cell in
raster 2 corresponds to another cell in raster 1 ? I have looked at
different functions like mosaic() and overlay() but those functions do not
seem to be applicable.

Thank you very much for any suggestions.

Juliane




? ? ? ?[[alternative HTML version deleted]]