############# RClimate Script: NSIDC_Monthly_Sea_Ice_Extent_Images.R    ##################
##   Download and process 1981 to 2012 Monthly Arctic SIE Images                       ##
##  Sept. 5, 2012: http://chartsgraphs.wordpress.com; DK O'Day                         ##
#########################################################################################
 library(animation)
## Establish working directory to place downloaded images and gif file
  setwd(getwd())
  where <- getwd()

## Monthly NSIDC Extent Immage Link
     # ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/Aug/N_198108_extn.png
  part_1 <- "ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/Aug/N_"
  part_3 <- "08_extn.png"

# Specify month number for animation  
  m <- "08"

# Loop through years to create link and download images
  for (y in 1981:2012) {  
    file_name <- paste(part_1, y, part_3, sep="")
    copy_name <- paste(where, "//asie",y,m,".png",sep="")
    download.file(file_name, copy_name, mode="wb")
   }

## copy last file c times to extend gif animation
 for (c in 1:2) 
      {
       file_name <- paste("asie2012",c, ".png",sep="")
       file.copy(from= copy_name, to = file_name, overwrite=T)
     }

## Use animation package to gernerate gif file
  ani.options(convert=shQuote('C:\\Program Files (x86)\\ImageMagick-6.7.9-Q16\\convert.exe'))
  ani.options(outdir = getwd())    # direct gif output file to working dir
  ani.options(interval= 0.70)
  im.convert("asie*.png", "asie_image_animation.gif")