[R-sig-Geo] raster: extract is empty with polygon

[Agustin Lobo]

I forgot to add that raster and vector do overlap in qgis (the vector
was actually digitized on top of the raster)
Agus

2011/3/24 Agustin Lobo <alobolistas at gmail.com>:
> Hi!
> I'm trying to calculate the mean values for a set of polygons.
> This is what I do:
>
> require(raster)
> require(rgdal)
> #SGRGBWBPS125F40
> #"read" tif file
> SGRGBF40 = brick("/media/TRANSCEND/MONTSENY2008/CALIBRACION2010/DigiPreprocess/TESTCASA/CALSEL/SGRGB/SGRGBWBPS125F40.tif")
>> SGRGBF40
> class       : RasterBrick
> filename    : /media/TRANSCEND/MONTSENY2008/CALIBRACION2010/DigiPreprocess/TESTCASA/CALSEL/SGRGB/SGRGBWBPS125F40.tif
> nlayers     : 3
> nrow        : 1760
> ncol        : 2640
> ncell       : 4646400
> projection  : NA
> min value   : 0 0 0
> max value   : 65535 65535 65535
> extent      : 0, 2640, 0, 1760  (xmin, xmax, ymin, ymax)
> resolution  : 1, 1  (x, y)
>> projection(SGRGBF40)
> [1] "NA"
>
> #read the shape file
> calibf2 = readOGR(dsn="/media/TRANSCEND/MONTSENY2008/CALIBRACION2010/DigiPreprocess/TESTCASA/CALSEL",layer="calibf2",stringsAsFactors=F)
>> projection(calibf2)
> [1] "+proj=utm +zone=31 +ellps=intl +units=m +no_defs"
>
>> projection(SGRGBF40) = projection(calibf2)
>
> But they do not overlap as shown by
>> plot(subset(SGRGBF40,1))
>> plot(calibf2,add=T)
>
> and the extracted object is empty
> #Calculate mean values for each polygon:
>> v <- extract(SGRGBF40, calibf2,fun=mean,nl=3)
>> summary(v)
>      Length Class  Mode
>  [1,] 0      -none- NULL
>  [2,] 0      -none- NULL
>  [3,] 0      -none- NULL
>  [4,] 0      -none- NULL
>  [5,] 0      -none- NULL
> etc
>
>> sessionInfo()
> R version 2.12.2 (2011-02-25)
> Platform: i486-pc-linux-gnu (32-bit)
>
> locale:
>  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
>  [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
>  [5] LC_MONETARY=C              LC_MESSAGES=en_US.UTF-8
>  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
>  [9] LC_ADDRESS=C               LC_TELEPHONE=C
> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> other attached packages:
> [1] rgdal_0.6-31 raster_1.7-8 sp_0.9-72
>
> loaded via a namespace (and not attached):
> [1] grid_2.12.2     lattice_0.19-17 tools_2.12.2
>