projectRaster: project a RasterLayer

Description

Project the values of a RasterLayer to a new RasterLayer with another coordinate reference system. projecExtent returns a RasterLayer with a projected extent, but without any values. This RasterLayer can then be used as 'to' RasterLayer in projectRaster. projectRaster computes values for the cells of the new RasterLayer.

Usage

projectRaster(from, to, method="ngb", filename="", ...) 
projectExtent(object, crs)

Arguments

from

a Raster* object

method

method used to compute values for the new RasterLayer. Either 'ngb' (nearest neighbor) or 'bilinear' (bilinear interpolation).

filename

character. output filename

...

additional arguments. See Details.

object

Extent or Raster* object

crs

Character or object of class CRS. PROJ4 type description of the coordinate reference system

Value

A RasterLayer or RasterBrick object, and, in some cases, the side-effect of a raster file written to disk.

Details

First create a template RasterLayer with an extent in the coordinate system of the crs you want to project to. You can use projectExtent for this or an existing Raster* object. Also set the number of rows and columns (or the resolution), and perhaps adjust the extent. The resolution of the output raster should normally be similar to that of the input raster. Then use that object to project the input RasterLayer to. Projection is performed using the PROJ.4 library accesed through the rgdal package. The best place to find PROJ4 coordinate reference system descriptions is http://www.spatialreference.org. You can also consult this page: http://www.remotesensing.org/geotiff/proj_list/ to find the parameter options and names for projections. Also see projInfo('proj'), projInfo('ellps'), and projInfo('datum') for valid PROJ.4 values. The following additional arguments can be passed, to replace default values for this function rll{ overwrite Logical. If TRUE, "filename" will be overwritten if it exists format Character. Output file type. See writeRaster datatype Character. Output data type. See dataType progress Character. "text", "window", or "" (the default, no progress bar) }

Examples

Run this code

# create a new (not projected) RasterLayer with cellnumbers as values
r <- raster(xmn=-110, xmx=-90, ymn=40, ymx=60, ncols=40, nrows=40)
r <- setValues(r, 1:ncell(r))
# proj.4 projection description
newproj <- "+proj=lcc +lat_1=48 +lat_2=33 +lon_0=-100 +ellps=WGS84"

# create a new RasterLayer with a projected extent (no values are transferred)
if (require(rgdal)) {
pr <- projectExtent(r, newproj)
# Adjust the cell size 
res(pr) <- 200000

# project the values of RasterLayer 'r' to the new RasterLayer 'projras'
pr <- projectRaster(r, pr)
# inverse projection, back to the properties of 'r'
inv <- projectRaster(pr, r)

## using a higher resolution and bilinear interpolation
# res(pr) <- 10000
# pr <- projectRaster(r, pr, method='bilinear')
# inv <- projectRaster(pr, r, method='bilinear')
# dif <- r - inv
# plot(dif)
}