[R] How to re-project ease( Equal Area Scalable Earth) grid with a ~25 km cylindrical projection to WGS84 0.25 degree?

Barry Rowlingson b.rowlingson at lancaster.ac.uk
Sat Jan 19 11:59:52 CET 2013

On Fri, Jan 18, 2013 at 5:11 PM, Jonsson <amen.alyaari at bordeaux.inra.fr> wrote:

> <-raster("C:\\Users\\aalyaari\\Desktop\\SM_RE01_MIR_CLF31D_20100812T000000_20100812T235959_246_001_7.nc",
> varname = "Soil_Moisture")
>         d:
>         class       : RasterLayer
>         dimensions  : 586, 1383, 810438  (nrow, ncol, ncell)
>         resolution  : 0.2603037, 0.2916659  (x, y)
>         extent      : -180, 180, -85.4581, 85.4581  (xmin, xmax, ymin, ymax)
>       coord. ref. : +proj=longlat +datum=WGS84
>         names       : Retrieved.soil.moisture.value
>            zvar        : Soil_Moisture
>        a <- spTransform(d, CRS ("+proj=longlat +ellps=WGS84 +datum=WGS84
> +no_defs"))
> but I got this error:
>      Error in function (classes, fdef, mtable)  :
>               unable to find an inherited method for function ‘spTransform’
> for signature ‘"RasterLayer", "CRS"’

 And what is the error telling you? That there's no method for
spTransform that applies to RasterLayers.

 To transform a raster from one projection to another you need to use
projectRaster from the raster package. Note that generally this can
involve warping a raster and interpolating the new values to get a
grid of cells in the new coordinate system.

 But... you were trying to do this:

 a <- spTransform(d, CRS ("+proj=longlat +ellps=WGS84 +datum=WGS84  +no_defs"))

where d was:

 coord. ref. : +proj=longlat +datum=WGS84

 - which is a no-op. The source and destination have the same
coordinate reference system. You need to tell raster what the
coordinate system of the source is. See ?projection - note this
doesn't change the raster or do any projection, its just to tell the
system what the coordinates in the data represent - lat,long or metres
or whatever..

I looked in the HDR file and saw nothing about the projection, so I
don't know how to specify what you've got.

 Also, you didn't point us to the .nc file you used in your example.

Also also, you should probably be posting to R-sig-geo.


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