[R-sig-Geo] Reproject raster from 0 360 to -180 180?

[Kranstauber, Bart]

Use rotate in the package raster see for example:
https://stat.ethz.ch/pipermail/r-sig-geo/2011-March/011155.html

Bart

On 07/09/2013 11:59 PM, Jorge Molinos wrote:
> 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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