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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:

generated with my code

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:

generated with Panoply

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)
13

Here are some ideas.

With base plot you can do

 plot(x, interpolate=TRUE)

You can also resample your data

 y <- disaggregate(x, 5, method='bilinear')

Or indeed smooth it using a focal operation

 y <- focal(x, w=matrix(1, 5, 5), mean)

Or a combination

 y <- disaggregate(x, 5)
 y <- focal(y, w=matrix(1, 5, 5), mean)

The question whether doing this is a good idea or not is another matter, that I'll leave to you to decide

  • Thanks for the fast input Robert. Apparently focal cannot be performed on rasterbricks, but disaggregate worked anyway. I tried to used it before, but the 'method' argument made a lot of difference. As of the "ethical" issue, the purpose of the plot is visualization only. No analysis is being done on the final product. I provided a more detailed justification on the R-SIG-GEO list at the link posted in the previous answer. Thank you again! – thiagoveloso Jun 29 '15 at 9:25

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