[R-sig-Geo] How to “smooth” a raster map

[Thiago V. dos Santos]

Dear all,

I am trying to create a map from raster data. The file came from a crop model, with resolution of 0.5 degree. Even when I disaggregate it (i.e. increase spatial resolution), the map looks really pixelated. I am trying to make it look better.
My current code produces this image: http://i.stack.imgur.com/WssPy.png

where I would like to "smooth" the data, by supressing the pixelated look. Some other visualization programs do this automatically, so I guess it should not be hard to reproduce using R. 

For example, this is the same file plotted using Panoply: http://i.stack.imgur.com/jXYI7.png

It doesn't look absolutely smooth, but at least it doesn't have the pixelated look neither. How to achieve a similar result in R? 

This is the code to reproduce my problem:

--------------------------------------------------------------------------
library(RCurl) 
library(rasterVis)

# Go to temp dir and download file - approx. 1.7M
old <- setwd(tempdir())

# download raster and shapefile
download.file('https://dl.dropboxusercontent.com/u/27700634/yield.nc', 'yield.nc', method='curl')
download.file('https://dl.dropboxusercontent.com/u/27700634/southern.zip', 'southern.zip', method='curl')
unzip('southern.zip', exdir='.')

# load southern Brazil shapefile
mapaSHP <- shapefile('southern.shp')

# load brick
b <- brick('yield.nc', level=16)

# create color scheme
mycols <- rasterTheme(region=colorRampPalette(brewer.pal(9,'Greens'))(100))

# use second brick layer to plot map
levelplot(b[[2]], margin = FALSE, main = "Rice yield in tons/ha", par.settings = mycols) +
layer(sp.lines(mapaSHP, lwd=0.8, col='darkgray'))

# return to your old dir
setwd(old)

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Thanks in advance for any input,
--
Thiago V. dos Santos
PhD student
Land and Atmospheric Science
University of Minnesota
http://www.laas.umn.edu/CurrentStudents/MeettheStudents/ThiagodosSantos/index.htm
Phone: (612) 323 9898