Lionel, Paco,
thanks for the quick answers.
Going through your suggestions I found that the function *resample {raster}
*that transfers values between non matching Raster* objects (in terms of
origin and resolution) does exactly what I need.
*resample* is actually embedded in the function *spatial_sync_raster* that
I had problems to run. When I tried to run it I got the following error
message:
Error in spatial_sync_raster(alt, slo, method = "ngb", verbose = FALSE) :
could not find function "expand"
*expand* is not part of the package climstats and I am not quite sure where
to find it...
But as said, *resample()* solved my problem.
Thanks!
Gabriele
On Thu, Sep 12, 2013 at 1:33 PM, Francisco Rodriguez Sanchez <
f.rodriguez.s...@gmail.com> wrote:
> Hi Gabriele,
>
> Try the spatial_sync_raster function in package climstats:
> https://r-forge.r-project.org/**projects/climstats/<https://r-forge.r-project.org/projects/climstats/>.
> It will align the projection, extent and resolution of your rasters all at
> once
>
> Hope it helps,
>
> Paco
>
>
> El 12/09/2013 11:59, Gabriele Cozzi escribió:
>
> Dear list,
>>
>> I was given three raster files with 'slope', 'aspect' and 'altitude' of my
>> study site. I realised that one of the three rasters (namely 'altitude')
>> has a slightly different raster cell resolution, which results in a
>> slightly different raster extent and does not allow me to raster::stack()
>> the three layers to create a single stack object.
>> I tried to change the raster resolution using raster::res() for the raster
>> 'altitude' but, when I subsequently cropped the three rasters with an
>> object of class extent, I still got different extents between "slope and
>> aspect" vs. "altitude".
>>
>> Any advice on how to solve this cell resolution incongruence is very
>> welcome.
>> Here below I report the output to make things more understandable.
>>
>> Thanks in advance,
>> Gabriele
>>
>>
>>
>> #----------------
>> #----------------
>>
>> aspect <- raster("~/Envir/aspect/prj.**adf")
>> slope <- raster("~/Envir/slope/prj.adf"**)
>> altitude <- raster("~/Envir/**20130508094222_992463356.tif")
>>
>> aspect ( N.B. 'slope' returns exactly the same attributes!)
>> #class : RasterLayer
>> #dimensions : 9813, 8428, 82703964 (nrow, ncol, ncell)
>> #resolution : 27.28532, 27.28532 (x, y)
>> #extent : 135446.9, 365407.6, 4345919, 4613669 (xmin, xmax,
>> ymin,
>> ymax)
>> #coord. ref. : +proj=utm +zone=38 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0
>> +units=m +no_defs
>>
>> altitude
>> #class : RasterLayer
>> #dimensions : 9812, 8428, 82695536 (nrow, ncol, ncell)
>> #resolution : 27.28532, 27.28677 (x, y)
>> #extent : 135446.9, 365407.6, 4345919, 4613656 (xmin, xmax,
>> ymin,
>> ymax)
>> #coord. ref. : +proj=utm +zone=38 +datum=WGS84 +units=m +no_defs
>> +ellps=WGS84 +towgs84=0,0,0
>>
>> ex <- extent(animal_locations)
>> ex
>> #class : Extent
>> #xmin : 257473.1
>> #xmax : 312499.1
>> #ymin : 4452821
>> #ymax : 4570717
>>
>> Before using the function raster.crop <- crop('raster_file', ex) to crop
>> all rasters to the same extent, I tried to change the resolution of
>> 'altitude' using
>>
>> res(altitude) <- 27.28532
>>
>> altitude
>> #class : RasterLayer
>> #dimensions : 9813, 8428, 82703964 (nrow, ncol, ncell)
>> #resolution : 27.28532, 27.28532 (x, y)
>> #extent : 135446.9, 365407.6, 4345905, 4613656 (xmin, xmax,
>> ymin,
>> ymax)
>> #coord. ref. : +proj=utm +zone=38 +datum=WGS84 +units=m +no_defs
>> +ellps=WGS84 +towgs84=0,0,0
>>
>> When I then run crop() for aspect and the new defined altitude I however
>> become different extents (i.e. ymin and ymax) despite now the dimensions
>> and resolutions are the same
>>
>> crop(aspect, ex)
>> #class : RasterLayer
>> #dimensions : 5054, 2749, 13893446 (nrow, ncol, ncell)
>> #resolution : 27.28532, 27.28532 (x, y)
>> #extent : 247480.5, 322487.8, 4442809, 4580709 (xmin, xmax,
>> ymin,
>> ymax)
>> #coord. ref. : +proj=utm +zone=38 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0
>> +units=m +no_defs
>> #names : prj
>> #values : -1, 359.8158 (min, max)
>>
>> crop(altitude, ex)
>> #class : RasterLayer
>> #dimensions : 5054, 2749, 13893446 (nrow, ncol, ncell)
>> #resolution : 27.28532, 27.28532 (x, y)
>> #extent : 247480.5, 322487.8, 4442823, 4580723 (xmin, xmax,
>> ymin,
>> ymax)
>> #coord. ref. : +proj=utm +zone=38 +datum=WGS84 +units=m +no_defs
>> +ellps=WGS84 +towgs84=0,0,0
>>
>> It also appears to me that by redefining res(altitude) I loose the actual
>> values assigned to each pixel. Is there an argument to assign to the new
>> pixels the value of the centre of the pixel?
>>
>>
>>
>>
> --
> Dr Francisco Rodriguez-Sanchez
> Forest Ecology and Conservation Group
> Department of Plant Sciences
> University of Cambridge
> Downing Street
> Cambridge CB2 3EA
> United Kingdom
> http://sites.google.com/site/**rodriguezsanchezf<http://sites.google.com/site/rodriguezsanchezf>
>
>
> ______________________________**_________________
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>
--
Gabriele Cozzi
Postdoctoral Research Associate
Population Ecology Research Group
http://www.popecol.org
Zurich University
Institute of Evolutionary Biology and Environmental Studies
Winterthurerstr. 190
8057 Zurich - Switzerland
E-mail: gabriele.co...@uzh.ch
Phone: +41(0)44 635 49 12
Fax: +41(0)16355711
http://www.ieu.uzh.ch
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