[R] Incorrect positioning of raster images on Windows

[Sharpie]

Michael Sumner-2 wrote:
> 
> I think there's something about the "discrete cell" versus "centre value"
> interpretation here, and you are pushing the "pixels" through R's graphics
> engine as well as whatever the png device has to do.
> 
> I can't enlighten you about the details of that, but by creating an image
> file more directly with "pixels as data" you can get the result exactly:
> 
> test <- matrix(c(0, 255), 3, 5)
> library(rgdal)
> ## transpose to get orientation right
> x <- image2Grid(list(x = 1:ncol(test), y = 1:nrow(test), z = t(test)))
> writeGDAL(x, "raster.png", driver = "PNG", type = "Byte")
> 
> 
> 
> On Mon, Oct 18, 2010 at 3:17 PM, Sharpie <chuck at sharpsteen.net> wrote:
> 
>>
>> I am working on dumping raster data from R into PNG files using
>> rasterImage().  I am working with a test matrix from the rasterImage()
>> example and using it to produce a PNG image with the following code:
>>
>>
>> # From the example for rasterImage(). A 3 pixel by 5 pixel b/w
>> checkerboard.
>> testImage <- as.raster(0:1, nrow=3, ncol=5)
>>
>> testImage
>>     [,1]      [,2]      [,3]      [,4]      [,5]
>> [1,] "#000000" "#FFFFFF" "#000000" "#FFFFFF" "#000000"
>> [2,] "#FFFFFF" "#000000" "#FFFFFF" "#000000" "#FFFFFF"
>> [3,] "#000000" "#FFFFFF" "#000000" "#FFFFFF" "#000000"
>>
>> png('test.png', width=5, height=3, units='px')
>>
>> # Just want the image, no margins, boarders or other fancy stuff.
>> par(mar = c(0,0,0,0) )
>> plot.new()
>> plotArea = par('fig')
>>
>> rasterImage(testImage, plotArea[1], plotArea[3],
>>  plotArea[2], plotArea[4], interpolate = FALSE )
>>
>> dev.off()
>>
>>
>> However, using R 2.12.0, 64 bit on Windows 7 I have a strange issue where
>> the image is shifted up by one row and to the left by one row.  In other
>> words, the bottom row of pixels is missing along with the right column.
>>  The
>> code works as I expect it to on OS X and Debian.
>>
>>
>> Am I misusing the plotting commands in some way or should I submit an
>> off-by-one bugreport to Bugzilla?
>>
>> Any suggestions or comments are most welcome.
>>
>> -Charlie
>>
>> -----
>> Charlie Sharpsteen
>> Undergraduate-- Environmental Resources Engineering
>> Humboldt State University
>> --
>> View this message in context:
>> http://r.789695.n4.nabble.com/Incorrect-positioning-of-raster-images-on-Windows-tp2999649p2999649.html
>> Sent from the R help mailing list archive at Nabble.com.
>>
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>> PLEASE do read the posting guide
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>> and provide commented, minimal, self-contained, reproducible code.
>>
> 
> 
> 
> -- 
> Michael Sumner
> Institute for Marine and Antarctic Studies, University of Tasmania
> Hobart, Australia
> e-mail: mdsumner at gmail.com
> 



Hi Micheal,

I appreciate the suggestion.  However, rgdal is very heavyweight and
installing the GDAL library is not a trivial operation automagically handled
`install.packages()` on every platform R supports.  As I am not doing
spatial analysis, I am very reluctant to add rgdal to the dependency list of
my package.

I would very much prefer to find the root cause of the difference in `png()`
behavior on Windows when compared to OS X and Linux.  If anyone on this list
has some insight to share, I would be very grateful to hear it.

I waffled a bit on whether to send this to R-help or R-devel, in the light
of day (as opposed to the foggy darkness that surrounds 2am) think it may be
more of an R-devel question.  Forwarding it there now.

-Charlie

-----
Charlie Sharpsteen
Undergraduate-- Environmental Resources Engineering
Humboldt State University
-- 
View this message in context: http://r.789695.n4.nabble.com/Incorrect-positioning-of-raster-images-on-Windows-tp2999649p3001166.html
Sent from the R help mailing list archive at Nabble.com.