Reproject raster from 0 360 to -180 180?

Hello everybody,

I have a raster that has longtitudes from 0 to 360 with the horizontal center at 180 longtitude

http://www.freeimagehosting.net/lr9rb

Pre_CCSM_r
class       : RasterLayer
dimensions  : 395, 320, 126400  (nrow, ncol, ncell)
resolution  : 1.125, 0.4294937  (x, y)
extent      : 0.50001, 360.5, -79.43527, 90.21475  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +datum=WGS84
data source : in memory
names       : layer
values      : 271.2439, 303.2426  (min, max)

I want to transform this to a new raster with -180, 180 longtitude range centred at Greenwich meridian (0) for comparisons/analysis with other raster files. I have tried cutting the original raster into two (using the meridian 180 as cutting value) and piece them back together but got sort of a mosaic raster instead

http://www.freeimagehosting.net/h5bxo

lonlat <- data.frame(xyFromCell(Pre_CCSM_r, 1:ncell(Pre_CCSM_r)))
lonlat <- cbind(lonlat, getValues(Pre_CCSM_r))
head(lonlat)

           x          y            getValues(Pre_CCSM_r)
1    1.06251 90              271.3698
2    2.18751 90              271.3698
3    3.31251 90              271.3698
4    4.43751 90              271.3698
5    5.56251 90              271.3698
6    6.68751 90              271.3698

lolaA <- as.matrix(lonlat[lonlat$x>180,])
lolaB <- as.matrix(lonlat[lonlat$x<=180,])
mydata <- rbind(lolaA,lolaB)
mydat <- matrix(mydata[,3], ncol=320,nrow=395,byrow=T)
Pre_Had <- raster(mydat,xmn=-180, xmx=180, ymn=-90, ymx=90,crs="+proj=longlat +datum=WGS84")

This is probably a very clumsy (obviously wrong) way of doing it so any help/advice will be very much appreciated.

Thanks!!

Jorge








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