[R-sig-Geo] attribing x-coordinates to map cells

[Roger Bivand]

On Fri, 8 Feb 2008, Milton Cezar Ribeiro wrote:

> Dear all,
>
> I have some ascii/grid files and I would like to save the x-coordinates into a new ascii/grid cells with the same dimentions that my input map. Below follow a temptative code.
>
> (file1 <-  paste(system.file(package = "adehabitat"),
>               "ascfiles/elevation.asc", sep = "/"))
> el <- import.asc(file1)
> image(el)
> ##el.xcoord<-  ### here is what I need

Roughly, using the sp SpatialGridDataFrame class:

library(adehabitat)
(file1 <-  paste(system.file(package = "adehabitat"),
                "ascfiles/elevation.asc", sep = "/"))
el <- import.asc(file1)
image(el)
library(sp)
cd <- dim(el)
cs <- rep(attr(el, "cellsize"), 2)
co <- c(attr(el, "xll"), attr(el, "yll"))
grd <- GridTopology(co, cs, cd)
SGDF <- SpatialGridDataFrame(grd,
   data=data.frame(asc=as.vector(el[,ncol(el):1])))
image(SGDF, "asc")
SGDF$x <- coordinates(SGDF)[,1]
co1 <- slot(slot(SGDF, "grid"), "cellcentre.offset")
el1 <- as.asc(as.matrix(SGDF["x"]), xll=co1[1], yll=co1[2],
   type="numeric")
image(el1)

If you only need the x coordinates of the non-missing cells, use the 
SpatialPixelsDataFrame class in addition. I guess that you could get there 
directly too.

Roger

>
> Kind regards,
>
> Miltinho
>
>
>
> para armazenamento!
>
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>
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-- 
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: Roger.Bivand at nhh.no