[R-sig-Geo] writeRaster to TIF changes raster maximum value

[Robert J. Hijmans]

I suspect that the original file has Byte values and that 255 is used,
perhaps erroneously, as NA. Can you give me access to the file?
Thanks, Robert

On Mon, Sep 16, 2013 at 8:10 AM,  <Guillaume.Drolet at mrn.gouv.qc.ca> wrote:
> Dear list members,
>
> I need your help trying to figure out why my raster's maximum value gets
> changed in the resulting TIF file from a call to the writeRaster function.
>
> I read here
> (http://r-sig-geo.2731867.n2.nabble.com/writeRaster-to-ascii-file-asc-td7584093.html#none)
>
> that this problem could be due to my version of GDAL (1.11dev released
> 2013/04/13). This is the GDAL version that is in my system's path. Don't
> know if this can help but when I load rgdal, I can read this:
>
> Loaded GDAL runtime: GDAL 1.9.2, released 2012/10/08
>
> Here are the details of my raster (myRaster) before calling writeRaster:
>
>   > raster(myRaster)
>
> class       : RasterLayer
> dimensions  : 7261, 7961, 57804821  (nrow, ncol, ncell)
> resolution  : 30, 30  (x, y)
> extent      : 457785, 696615, 5147085, 5364915  (xmin, xmax, ymin, ymax)
> coord. ref. : +proj=utm +zone=18 +datum=WGS84 +units=m +no_defs
> +ellps=WGS84 +towgs84=0,0,0
> data source : E:\temp\Fmask\Image\L71015027_02720000730_B10.tif
> names       : L71015027_02720000730_B10
> values      : 0, 255  (min, max)
>
>
> I crop "myRaster" using the crop function with a bounding box and then I
> save the cropped raster as a TIF with:
>
>   > writeRaster(rc, "myCroppedRaster.tif", datatype = "INT2S")
> rgdal: version: 0.8-11, (SVN revision 479M)
> Geospatial Data Abstraction Library extensions to R successfully loaded
> Loaded GDAL runtime: GDAL 1.9.2, released 2012/10/08
> Path to GDAL shared files:
> C:/Users/Utilisateur/Documents/R/win-library/3.0/rgdal/gdal
> GDAL does not use iconv for recoding strings.
> Loaded PROJ.4 runtime: Rel. 4.7.1, 23 September 2009, [PJ_VERSION: 470]
> Path to PROJ.4 shared files:
> C:/Users/Utilisateur/Documents/R/win-library/3.0/rgdal/proj
>
> class       : RasterLayer
> dimensions  : 3628, 3994, 14490232  (nrow, ncol, ncell)
> resolution  : 30, 30  (x, y)
> extent      : 457785, 577605, 5147085, 5255925  (xmin, xmax, ymin, ymax)
> coord. ref. : +proj=utm +zone=18 +datum=WGS84 +units=m +no_defs
> +ellps=WGS84 +towgs84=0,0,0
> data source : E:temp\myRaster.tif
> names       : myRaster
> values      : 0, 254  (min, max)
>
>
> As shown in the output from writeRaster, the maximum value in the output
> TIF file is now 254. I double-checked and
> there are pixels with value 255 in the cropped area of the original
> raster so the maximum value shouldn't be 254 but 255.
>
> Here's the output of my sessionInfo():
>
> R version 3.0.1 (2013-05-16)
> Platform: x86_64-w64-mingw32/x64 (64-bit)
>
> locale:
> [1] LC_COLLATE=French_Canada.1252  LC_CTYPE=French_Canada.1252
> LC_MONETARY=French_Canada.1252
> [4] LC_NUMERIC=C                   LC_TIME=French_Canada.1252
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> other attached packages:
> [1] rgdal_0.8-11  raster_2.1-49 sp_1.0-13
>
> loaded via a namespace (and not attached):
> [1] grid_3.0.1      lattice_0.20-15 tools_3.0.1
>
> I thank you in advance for any hint that could help me solve this
> problem.
>
> Guillaume
> --
> Guillaume Drolet ing.f M.Sc.
> Chercheur en télédétection et dynamique forestière
> Direction de la recherche forestière
> Ministère des ressources naturelles du Québec
> 2700, rue Einstein, C.RC.335
> Québec (Québec), Canada G1P 3W8
> T : +1 418 643 7994 # 6727
> F : +1 418 643 2165
> guillaume.drolet at mrn.gouv.qc.ca
> http://www.mrn.gouv.qc.ca/forets
>
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