[R] Incorrect positioning of raster images on Windows

[Paul Murrell]

Hi

This is a rounding (truncation) problem.
Working on a fix.

Paul

Sharpie wrote:
> 
> 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.
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
>>> 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

-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/