[R-sig-Geo] Crop a raster using a shapefile

[Thiago Veloso]

  Dear all,

  When cropping a raster using a shapefile, through 'crop' function from "raster" package, only the extent is taken into account:

> r<-raster("lai2011361.Lai_1km.tif")
> extent(r)

class       : Extent 
xmin        : -104.4326 
xmax        : -29.99736 
ymin        : -40.00064 
ymax        : 10 

> br<-readShapePoly("/mnt/disco3/MODIS/shapes/brazil.shp")

> extent(br)

class       : Extent 
xmin        : -73.83943 
xmax        : -34.8581 
ymin        : -33.77086 
ymax        : 5.38289 

> c<-crop(r,br)

> extent(c)
class       : Extent 
xmin        : -73.83772 
xmax        : -34.85554 
ymin        : -33.76852 
ymax        : 5.38428 

  However, the cropped raster is rectangular. Is there any way to keep also the "shape" of a shapefile (and not only its extent) when performing this kind of crop operation?

  Thanks in advance,
  Thiago.