[R] Converting the graphics window to a data matrix

[Beutel, Terry S]

Thanks Barry. I have now got as far as creating the png (or gif or tiff) images (as per your suggestions). But I am unable to work out how to convert each to a 2 dimensionional numeric matrix showing the spatial distribution of occupied/unoccupied pixels in R. Any suggestions anybody? 
Thanks

Terry

-----Original Message-----
From: b.rowlingson at googlemail.com [mailto:b.rowlingson at googlemail.com] On Behalf Of Barry Rowlingson
Sent: Thursday, 19 May 2011 4:19 PM
To: Beutel, Terry S
Cc: r-help at r-project.org
Subject: Re: [R] Converting the graphics window to a data matrix

On Thu, May 19, 2011 at 5:19 AM, Beutel, Terry S <Terry.Beutel at deedi.qld.gov.au> wrote:
> I'm wondering if anyone is aware of a way to take what is visible in 
> the R graphics window, pixelate it, and express that pixellation in a 
> numeric matrix. For example, I am using the following command to 
> create a  black (present) and white (absent) spatial simulation of 
> grass tussock distribution.
>
>>
> symbols(x=runif(100,-.5,1.5),y=runif(100,-.5,1.5),circles=runif(100)/3
> 0,
> inches=F,bg=1,xlim=c(0,1),ylim=c(0,1))
>
> What I would like to end up with is a 2 dimensional matrix that 
> indicates presence/absence of grass in any given pixel as per the 
> image generated from the above graphics plot.

 Instead of drawing to the screen, you can use the 'png' function to create a graphics device that "draws" to an image file. Then you can read that image file into R and get it as a matrix.

 You probably also want to set some of the margin and axis parameters so the plotting region fills the whole device, and you dont have the axes and tick marks etc confusing the matrix.

 That's some pointers for starters. I've not had breakfast yet...

Barry


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