[R] Plotting using image files

[Henrik Bengtsson]

Mike Saunders wrote:
> This is a strange request, but I want to build a scatterplot using different image files (jpegs, gif, etc.) as the plot symbols.  I have thought about setting this up using a very large layout matrix, but I thought someone might have a better approach.  Furthermore, is there any way to have R paste an image file into a specific coordinate within a scatterplot?

I don't think this is possible using the default graphics engine in R, 
but here is another solution using ImageMagick 
(http://www.imagemagick.org/) calls from R.  I once needed something 
similar to highlight certain cities on a Swedish map given their 
longitute/latitude coordinates.  The map was given as bitmap image. 
Given a few reference citites with known longitute/latitude and pixel 
coordinates I used a quick-and-dirty 2d-loess to get a 
longitute/latitude-to-pixel coordinate mapping.  This way I could find 
the pixel coordinates for new citites and then I used ImageMagick to add 
colorful discs in the original bitmap image.  The result is as shown on 
http://www.maths.lth.se/kovalevsky/skolor/.  It is quite easy to write 
wrapper functions in R that calls ImageMagick via system() calls.  My 
code is in http://www.maths.lth.se/kovalevsky/skolor/updatemap.R, but 
please don't ask me to explain how it works, because I don't have the 
time available for that. Basically, ImageMagick's 'convert' command 
provide command line options to add discs ("circles"), lines etc in 
different colors to existing images.  Make sure to set a pen color 
before drawing.  I think it allows you to "draw" using other bitmap 
image too.  My R code generates a convert call string which is called at 
the end.

Hope this helps a bit

Henrik Bengtsson


> Thanks in advance,
> Mike 
> 
> 
> Mike Saunders
> Research Assistant
> Forest Ecosystem Research Program
> Department of Forest Ecosystem Sciences
> University of Maine
> Orono, ME  04469
> 207-581-2763 (O)
> 207-581-4257 (F)
> 
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