On Sat, 9 Aug 2008, Rainer M Krug wrote:
Hi
I have a SpatialGridDataFrame-class (grd) and a
SpatialPolygonsDataFrame (polyg) with more then one attribute columns,
i.e.
names(slot(polyg, "data"))
results in
"a", "b", "c", ... "z"
I want to use overlay to convert polyg into a grid, by assigning the
values of attribute column "d" to the grid.
Is it possible to specify the column name in the following overlay statement:
d <- overlay(grd, polyg)
grd[[1]] <- d
Not like that. Here with grd a SpatialGrid:
library(sp)
library(maptools)
polyg <- readShapeSpatial(system.file("shapes/sids.shp",
package="maptools")[1], IDvar="FIPSNO",
proj4string=CRS("+proj=longlat +ellps=clrk66"))
grd <- Sobj_SpatialGrid(polyg)$SG
d <- overlay(grd, polyg)
# d contains the indices of the Polygons object into which each cell
# centre falls, or NA
summary(d)
names(polyg)
v <- polyg$SID74[d]
# use d to index the variable of interest
# if grd had been a SpatialGridDataFrame, just assign "$<-", or:
grdd <- SpatialGridDataFrame(grid=slot(grd, "grid"),
data=data.frame(SID74=v), proj4string=CRS(proj4string(grd)))
summary(grdd)
image(grdd)
spplot(polyg, "SID74")
Roger
results in the values of the attribute column "d" in grd[[1]]?
Thanks,
Rainer
--
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: [EMAIL PROTECTED]
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