[R] Draw a circle on a filled.contour() plot

[Duncan Murdoch]

On 12/17/2006 7:06 AM, Webmaster wrote:
> Hi all,
> 
> I'm trying to use symbols() to draw a circle of a given radius at a  
> given position onto a filled.contour() plot. The commands I issue are:
> 
>> filled.contour(y,x,z,levels=seq 
>> (0.02,1.0,len=50),color.palette=colorRampPalette(c 
>> ("blue","yellow","red")),title=title(main="",xlab="",ylab=""))
>> symbols(0.62,0.0,circles=c(2.5),add=TRUE,inches=FALSE
> 
> As can be seen on the resulting PDF file (http://www.eleves.ens.fr/ 
> home/coudert/hist_2d.pdf), the circle appears to have the right  
> radius but its center is not the correct one [0.62, 0]. What am I  
> missing here?

There's a note on the man page about this:

The output produced by 'filled.contour' is actually a combination
      of two plots; one is the filled contour and one is the legend.
      Two separate coordinate systems are set up for these two plots,
      but they are only used internally - once the function has returned
      these coordinate systems are lost.  If you want to annotate the
      main contour plot, for example to add points, you can specify
      graphics commands in the 'plot.axes' argument.  An example is
      given below.

Duncan Murdoch
> 
> Thanks for your help,
> FX
> 
> PS: complete input (5 lines), data file for the contour plot and PDF  
> result on my system can be found at:
> Data file: http://www.eleves.ens.fr/home/coudert/hist_2d
> R script: http://www.eleves.ens.fr/home/coudert/hist_2d.R
> PDF result: http://www.eleves.ens.fr/home/coudert/hist_2d.pdf
> 
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