Re: [R] Finding the "height of a line of text" for axis

From: Paul Murrell <p.murrell_at_auckland.ac.nz>
Date: Thu 31 Mar 2005 - 10:17:19 EST

Hi

Steven J. Murdoch wrote:
> Thanks for your reply.
>
> On Wed, Mar 30, 2005 at 08:03:10AM -0600, Marc Schwartz wrote:
>

>>or even something like this:
>>
>> plot(1:5, axes = FALSE)
>> axis(1, col.axis = "white", col = "red", tcl = 1)
>> axis(1, col.axis = "white", col = "white", tcl = 0)
>> axis(2, col.axis = "white", col = "red", tcl = 1)
>> axis(2, col.axis = "white", col = "white", tcl = 0)

>
>
> This is the effect I am trying to achieve. I did try the route of
> overdrawing in white, but decided against it. The reason I haven't
> used that, is that firstly I wasn't sure if there would be some
> rounding error in a printer which would cause the background to
> appear. Secondly, the end of the ticks look weird due to the different
> line end types:
> http://www.cl.cam.ac.uk/users/sjm217/volatile/r-lineend.png
>
> Changing to square caps might help, but I was hoping there would be a
> nice solution that would let me keep round caps. Any suggestions?

The function GConvertYUnits() (and the functions it calls) are in the file graphics.c (same directory as plot.c), but I'd book a week off before trying to trace the calculations performed therein.

A more accurate calculation than ...

   l<-par("cxy")[2]*par("tcl")
... is ...

   l<-par("cin")[2]/par("pin")[1]*diff(par("usr")[1:2])*par("tcl") ... but that still needs par("cex") and a par("mex") multipliers to be (possibly) fully par() compliant. This general replicate-par()-in-R-code route is likely to be a recipe for unhappiness.

Some sort of overplotting trick is probably a better choice if you can cope with the compromise. The following variation on Marc's suggestion might provide a slight improvement:

  plot(1:5, axes = FALSE)
  axis(1, col.axis = "white", col = "red", tcl = 1)
  axis(2, col.axis = "white", col = "red", tcl = 1)
  box(col="white")

Something like box(col="white", lwd=1.1) could be used to allay fears of axes peeking through from behind.

Paul

-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul@stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/

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Received on Thu Mar 31 10:22:41 2005

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