[R] TeachingDemos question: my.symbols() alignment problems in complicated layout

[Paul Murrell]

Hi


maria at meteo.mcgill.ca wrote:
> Hello,
> 
> After usefull suggestions by Paul Murrell, i have been trying to use
> my.symbols to plot arrows of varying angles on my plot in order to create
> a time series of wind direction... however,i have been unable to figure
> out how the allignment of symbols works...
> 
> below i have included a simplified code that illustrates my problem:
> (i am creating a .ps file ... so i've included this in my mock code, in
> case it might be part of the problem...)
> 
> ############################# TEST CODE #################################
> 
> postscript("test.ps", horizontal=FALSE, width=7.5,
> height=11.5,pointsize=10, paper = "special" )
> 
> library(TeachingDemos)
> 
> opar <- par(omi=c(0,0.1,0.7,0.1),xpd=T,mar=par()$mar+c(0,-1.5,-1,5))
> 
> layout_mat = matrix(c(1,2,3,4),nrow=4,ncol=1,byrow=TRUE)
> 
> my_layout <-
> layout(layout_mat,widths=c(1,1,1,1),heights=c(1.0,0.45,1.0,1.2),respect=FALSE)
> 
> plot(1,1)
> plot(2,2)
> plot(3,3)
> plot(1:100,rep(c(9,1.5,2,8),25))
> points(40,4,col="red")
> points(50,8,col="red")
> my.symbols(40,4,ms.polygon,n=3,inches=0.2,add=TRUE)
> my.symbols(40,4,ms.arrows,angle=pi/2,inches=0.2,add=TRUE)
> my.symbols(50,8,ms.arrows,angle=pi/4,inches=0.2,add=TRUE)
> dev.off()
> 
> ######################## END of TEST CODE ###############################
> 
> If i look at the output test.ps ... the first symbol is exactly where i
> want it to be i.e. at x=40,y=4 ... while the position of the two other
> ones is offset by some mysterious(!!) value
> 
> then if i comment out the first my.symbols(...) command... the second
> symbol is at the right place, while the third is offset ...etc
> 
> However if i simply do:
> 
> plot(1:100,rep(c(9,1.5,2,8),25))
> points(40,4,col="red")
> points(50,8,col="red")
> my.symbols(40,4,ms.polygon,n=3,inches=0.2,add=TRUE)
> my.symbols(40,4,ms.arrows,angle=pi/2,inches=0.2,add=TRUE)
> my.symbols(50,8,ms.arrows,angle=pi/4,inches=0.2,add=TRUE
> 
> 
> then everything is exactly where i want it ... suggesting there is a
> problem with the layout ???


I think the issue is that my.symbols() does a lot of this ...

            op <- par(no.readonly = TRUE)
            on.exit(par(op))

... which is not absolutely guaranteed to get you back to where you
started (see the comment in the 'Value' section of the help page ?par).
   Fixing that will need the cooperation of the author of TeachingDemos.

Here are a couple of options:

(i)  use the 'gridBase' package and do these arrow annotations using the
'grid' package, which allows you to control coordinate systems in a more
rational manner.  There's an example (perhaps slightly more complicated
than you need) in:
http://cran.r-project.org/doc/Rnews/Rnews_2003-2.pdf

(ii) draw your main plot using 'lattice' and the annotations using
'grid' or possibly 'grImport'.  There's a hint of an example of the
latter on slide 18 of:
http://www.stat.auckland.ac.nz/~paul/Talks/import.pdf

(iii) draw the whole thing using 'grid'.  You can start to get
acquainted with grid here:
http://www.stat.auckland.ac.nz/~paul/RGraphics/chapter5.pdf

Unfortunately, all of these require a reasonable amount of extra
learning on your part.

Paul


> Any help would be really appreciated,
> Thank You a lot,
> maria
> 
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-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/