[R-sig-Geo] spTransform changes the class

[Michael Sumner]

spTransform cannot reproject a grid - this will (usually) requires
destructive resampling of the data to a completely new grid. There are
functions in the raster package to do this: projectRaster.

I think this would work, but there may be important details that you
will need to investigate:

raster.eugrd025 <- raster(eugrd025)

eugrd025EFDC <- projectRaster(raster.eugrd025,
CRSobj=CRS(projection(eugrd025EFDC_SPDF)))

On Fri, Jul 2, 2010 at 1:40 AM, Agustin Lobo <alobolistas at gmail.com> wrote:
> Hi!
>
> I use spTransform to reproject:
>
>> class(eugrd025)
> [1] "SpatialGrid"
> attr(,"package")
> [1] "sp"
>
>> projection(eugrd025)
> [1] "+proj=longlat +ellps=WGS84"
>
>> eugrd025EFDC <- spTransform(eugrd025, CRSobj=CRS(projection(eugrd025EFDC_SPDF)))
>
>> projection(eugrd025EFDC)
> [1] "+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000
> +ellps=GRS80 +units=m +no_defs"
>
> This is good, but:
>> class(eugrd025EFDC)
> [1] "SpatialPoints"
> attr(,"package")
> [1] "sp"
>
> Why is the class changed to SpatialPoints? I need a grid object for
>> eugrd025EFDCr <- raster(eugrd025EFDC)
>> Br025 <- resample(Br,eugrd025EFDCr)
>
> don't I?
>
> I also have the problem that the CRS of eugrd025EFDCr is not conserved:
>> projection(Br)
> [1] "+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000
> +ellps=GRS80 +units=m +no_defs"
>
>> projection(eugrd025EFDC)
> [1] "+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000
> +ellps=GRS80 +units=m +no_defs"
>
>> projection(eugrd025EFDCr)
> [1] "NA"
>
> which I fix with
>> projection(eugrd025EFDCr) <- CRS(projection(eugrd025EFDC))
>
> and repeat
>> Br025 <- resample(Br,eugrd025EFDCr)
>
> Anyway, I get a much coarser raster than I want:
>> dim(Br025)
> [1] 10 10  1
>
> because
>> dim(eugrd025EFDCr)
> [1] 10 10  1
>
> While it should be 180x100:
>
>> summary(eugrd025EFDC)
> Object of class SpatialPoints
> Coordinates:
>       min     max
> s1 2498538 6561151
> s2 1327858 4313263
> Is projected: TRUE
> proj4string :
> [+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80
> +units=m +no_defs]
> Number of points: 18000
>> dim(Br025)
> [1] 10 10  1
>
>> summary(eugrd025)
> Object of class SpatialGrid
> Coordinates:
>              min    max
> coords.x1 -10.125 34.875
> coords.x2  34.875 59.875
> Is projected: FALSE
> proj4string : [+proj=longlat +ellps=WGS84]
> Number of points: 2
> Grid attributes:
>  cellcentre.offset cellsize cells.dim
> 1               -10     0.25       180
> 2                35     0.25       100
>
> Is eugrd025EFDCr wrong because class(eugrd025EFDC) has been changed
> from SpatialGrid to SpatialPoints?
>
> Agus
>
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