[R-sig-Geo] spTransform changes the class

[Robert J. Hijmans]

The general idea is that for changing the projection of a raster you
provide the input RasterLayer and a Raster object with the spatial
parameters (projection, extent, resolution) to which it should be
transformed. For the latter, you can use the RasterLayer that you want
to project the input data to (I call it 'x').

prjgrd <- projectRaster(eugrd025, x, method='bilinear')

Note that it should *not* be necessary to resample after projection
because projecting a raster already implies resampling.

Robert

On Thu, Jul 1, 2010 at 8:48 AM, Michael Sumner <mdsumner at gmail.com> wrote:
> Ah, sorry that was completely wrong. I think this is right, but still untested:
>
> raster.eugrd025 <- raster(eugrd025)
>
> pr <- projectExtent(raster.eugrd025, projection(eugrd025EFDC_SPDF))
>
> eugrd025EFDC <- projectRaster(raster.eugrd025, pr)
>
>
>
> On Fri, Jul 2, 2010 at 1:46 AM, Michael Sumner <mdsumner at gmail.com> wrote:
>> 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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>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>
>>
>
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