[R-sig-Geo] Overlay-ing two grids

[Paul Hiemstra]

Hi Renaud,

Take a look at the pointsToRaster() function in the raster package.

cheers,
Paul

Renaud Lancelot wrote:
> Dear all,
>
> I have two "nested" grids (SpatialGridDataFrame) looking like this:
>
> prj <- "+proj=utm +zone=28 +ellps=WGS84 +datum=WGS84 +units=m +no_defs"
> gt1 <- GridTopology(c(5, 5), c(10, 10), c(100, 100))
> gt2 <- GridTopology(c(50, 50), c(100, 100), c(10, 10))
> band1 <- sample(c(0, 1), replace = TRUE, size = 10000)
> sgdf1 <- SpatialGridDataFrame(gt1, data.frame(band1), CRS(prj))
> sgdf2 <- SpatialGridDataFrame(gt2, data.frame(band1=rep(0, 100)), 
> CRS(prj))
> ## Graphic display
> spplot(sgdf1, scales = list(draw = TRUE),
>        panel = function(...){
>            panel.gridplot(...)
>            sp.grid(sgdf2, col = 0)
>            })
>
> I want to compute the mean (and other statistics) of sgdf1 at data$band1 
> according to the cells defined in sgdf2. How can I do that ? I tried 
> to use overlay, without success:
>
> > sgdf3 <- overlay(sgdf1, sgdf2, fn = mean)
> > sgdf3 at data$band1
>   [1] 1 0 0 0 0 0 1 1 1 0 0 1 0 0 0 0 0 1 1 0 1 0 1 1 0 1 0 0 0 0
>  [31] 0 0 1 0 1 1 1 0 0 0 0 0 0 1 0 1 1 0 0 0 1 0 1 0 1 0 1 1 0 0
>  [61] 1 1 0 1 1 1 1 0 0 0 1 1 0 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0
>  [91] 1 0 1 1 1 0 1 0 1 0
>
> All the best,
>
> Renaud
>
>
>


-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
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3508 TC Utrecht
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http://intamap.geo.uu.nl/~paul