[R] Alignment when rotating text and symbols

Prof Brian Ripley ripley at stats.ox.ac.uk
Tue Jul 29 12:26:56 CEST 2003

On Tue, 29 Jul 2003, p.b.pynsent wrote:

> I wanted to annotate some points on lines, above and below the lines.  
> I thought the easiest way would be to use text() and two pos values.
> However I found when the text was rotated the space and alignment 
> between the point and the text did not remain constant. The following 
> code illustrates the problem:

You are rotating the text about its centre, but pos is not in the 
rotated frame, as I read it, so why should this be rotation-invariant?


> plot(1:10, type="n")
> text(5,5, "a bit of text")
> text(5,5, "a bit of text", pos=1)
> text(5,5, "a bit of text", pos=1, srt=45)

to see the effect of pos and srt.  You go down then rotate, not rotate and 
then go down.

> x <- c(0,10.)
> y <- c(0,10.)
> offset <- 3
> centre <- 5
> plot(x,y, xlim=range(x), ylim=range(y),type="n", xlab="",ylab="", 
> main="",xaxt="n",yaxt="n")
> for (i in (seq(0, 340, by=45))	)
> 	{
> 	px <- centre + cos((i*pi)/180) * offset
> 	py <- centre + sin((i*pi)/180) * offset
> 	text(px, py,
> 	labels=substitute(that%->%phantom(1),list(that=i)), pos=1, col="blue", 
> cex=0.7, srt=i)
> 	text(px, py,
> 	labels=substitute(that%<-%phantom(1),list(that=i)), pos=3, 
> col="blue",cex=0.7,srt=i)
> 	lines(px, py, type="p", col="black") #just for reference
> 	}
> What have I done wrong?
> In addition, on my screen, the arrow symbols do not rotate at all 
> although they do on the pdf image.
> (R version 1.71,  MacOS X 10.2.6)

*WHICH* Mac port of R?  There are two!

The lack of rotation is a limitation of the (unspecified) graphics device
of your (unspecified) port, whichever it is: it works on Linux and
Windows, for example, so I would expect this to work on an X11 device on
the Darwin port.

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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