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

[Torleif Markussen Lunde]

Hi

I guess you could also try something like:

# First of all
showMethods(overlay)

# Than, one possibility:
ovrl <- overlay(as(sgdf2, "SpatialPixelsDataFrame"), 
		as(sgdf1, "SpatialPointsDataFrame"))

# aggregate by the ovrl index
aggMean <- aggregate(slot(sgdf1, "data"), 
		     by = list(ovrl), 
		     FUN = mean)$band1
# make a new SpatialGridDataFrame:
sgdf3 <- SpatialGridDataFrame(gt2, 
			      data.frame(band1=aggMean), 
			      CRS(prj))

Best wishes
Torleif


On Tuesday 22 December 2009 10:52:50 Paul Hiemstra wrote:
> 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
>