# [R] Alignment when rotating text and symbols

p.b.pynsent p.b.pynsent at bham.ac.uk
Tue Jul 29 13:38:19 CEST 2003

```Dear Prof Ripley,
Many thanks for this response. I do not understand how your example
addresses my problem. Basically what concerns me is the relationship
between pos=1 and pos=3 upon rotation, if I take your example and
modify it slightly to be at srt=180 I would expect to get an inverted
view of srt=0.
This is not the case, the spacing between the two lines of text becomes
so different that at 180 degrees the text now fits within the non
rotated text. At intermediate values the text remains aligned to the
vertical of the plot rather than to the angle of rotation and so
becomes offset.

What I had hoped for was what I get with srt=0, rotated as whole so it
looked the same but was just rotated to the specified angle.

plot(1:10, type="n")
text(5,5, "a bit of text", pos=1)
text(5,5, "a bit of text", pos=3)
text(5,5, "a bit of text", pos=1, srt=180)
text(5,5, "a bit of text", pos=3, srt=180)

Paul

On Tuesday, July 29, 2003, at 11:26  am, Prof Brian Ripley wrote:

> 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?
>
> Try
>
>> 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.
>
Yes this is ambiguous,sorry.  Not 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
>
>

```