Change coordinates to a series of rasters with multiple layers in R

问题

I have a problem with a climate projections database organised in raster files.

Each file contains information (about precipitation for instance) for one year, organised as follow: 365 layers of data for a grid of 0.5 degrees going from 0 to 360 lon and from 65 to -65 lat. Each layer is a grid with 720 columns and 260 rows.

class : RasterStack dimensions : 260, 720, 187200, 365 (nrow, ncol, ncell, nlayers) resolution : 0.5, 0.5 (x, y) extent : -0.25, 359.75, -65.25, 64.75 (xmin, xmax, ymin, ymax) coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0

I need to reorganise these information shifting the right part of the grid and putting Greenwich in the middle of the database (instead of having a system going from 0°to 360° I need to reorganise the infomation from -180 and +180°). The reorganization cannot be limited to a normal shift of the entire layer: I neet to take the part of the layer 180°/360° and moving it to -180°/0°. This action has to be done for each of the layers of each of the files (corresponding to the years) of the database.

I drafted a loop for this action, but I have some problems and takes a huge amount of time to be processed. Do you have any better idea?

`setwd ("E:/directory") #inside the directory there are a list of layerrasterfile.nc

filelist<-list.files(pattern=".nc")
n<-length(filelist)
clim_data<-vector("list",n)

for (j in 1:65){  # or (j in filelist), for this action only 65 files
clim_data<-stack(filelist[j])

e<-extent(0,360,-65,65)
extent(clim_data)<- c(0,360,-65,65)

yr_name <-substr(filelist,30,34) #with this I want to capture the year contained in the file name (2206 2007 and so on)

rdataname <- paste(paste(yr_name, sep='_'), ".Rdata", sep="")
rdataname <- rdataname[j]
form<-function(clim_data)
{
 for (i in 1:260) 
  {
    AA<-clim_data[i,]
    HH<-AA[c(361:720,1:360),]
    clim_data[i,]<-HH

  }
  save(cmlim_data, file = rdataname[j]) #with this I want to save a .Rdata file for each of the years in order to proceed to the extraction of the information with a second loop.
}

form(clim_data)
}`

Thanks a lot.

回答1:

This should work:

setwd ("E:/directory")

filelist <- list.files(pattern=".nc")
for (j in filelist){
  clim_data <- stack(j)
  clim_data <- rotate(clim_data)

  yr_name <- substr(j, 30, 34)
  rdataname <- paste(paste(yr_name, sep='_'), ".Rdata", sep="")

  save(cmlim_data, file = rdataname)
}

来源：https://stackoverflow.com/questions/24884694/change-coordinates-to-a-series-of-rasters-with-multiple-layers-in-r

标签

raster