[R-sig-Geo] problems to stack() rasters due to different pixel resolution and raster extent

[Francisco Rodriguez Sanchez]

Hi Gabriele,

Try the spatial_sync_raster function in package 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