[R] Maps and plotting

Prof Brian Ripley ripley at stats.ox.ac.uk
Thu Oct 14 13:04:59 CEST 2004

On Thu, 14 Oct 2004, Barry Rowlingson wrote:

> Shawn Way wrote:
> >  At our facility we have multiple sample points that are sampled on any
> > given day.  What I would like to do is create a map of the facility with
> > the sample points (and point labels) and when we have out of
> > specification results, place a transparent dot over the area on the map.
> > As the number of OOS results builds up, I envision the dot getting
> > darker.
> > 
>   Over what timescale? This sounds like it could be an interactive, 
> real-time on-line monitoring thing. Is it?
>   In which case R's graphics devices might not be good enough, and you'd 
> be better off using a TclTk graphics canvas.
>   library(tcltk) and read the docs!
>   Another idea, if all you are doing is updating a daily image, would be 
> to use a language like Python, and the Python Imaging Library (PIL) to 
> draw pretty graphs.
>   I've done something similar that produces daily maps of disease 
> incidence, but I used different size and colour circles and not 
> transparency, so I just used base R graphics and produced a PNG file. If 
> I wanted transparency I'd probably use Python/PIL, which can handle 
> alpha channels.

I think this may mean *translucent* dots.  R has been able to do 
transparent dots for a very long time, but PNG cannot handle 
translucency.  On devices (e.g. pdf) which can, you can do this as of R 

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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