[R] pie EPS BB

[(Ted Harding)]

Greetings all!
I'm facing a puzzle I have not been able to solve.
I need to make an EPS of a pie-chart (Yes, I know;
please don't bother to tell me! I just need to ...).

I'm trying to do it with pie(), and I want to have
just the plain pie-chart with no annotations. So far
so good: "labels=rep(NA,...)" will do it.

But I want to have it output to an EPS file with the
BoundingBox *exactly* containing the pie-chart, i.e.
the pie-chart boundary touches the four sides of the
BoundingBox, and its centre is at the centre of the
BoundingBox. This is the puzzle I have not been able
to solve.

Here is an example of the sort of thing I have been trying.

pcts <- c(3.0,2.0,0.4,10.0,12.0,3.0,39.0,14.0,7.0,9.6)
postscript("piecharttest.eps",horizontal=FALSE,
           paper="special",width=3.0,height=3.0)
pie(pcts, clockwise=TRUE, labels=rep(NA,10), radius=1.0)
dev.off()

With
  pie(pcts, clockwise=TRUE, labels=rep(NA,10), radius=1.0)
  lines(c(-1,1,1,-1,-1),c(-1,-1,1,1,-1))
I can see that the chart exactly fits inside a box with
side 2 and centre (0,0). So far so good. But this box is
not centred in the X-window device (somewhat up, and
somewhat to the right, from centre).

The result from the above postscript() command is a file
with

%%DocumentMedia: special 216 216 0 () ()
%%BoundingBox: 0 0 216 216

(where of course "216" means 3*72 points = 3 inches), and
when this is displayed (using 'gv') I see the pie-chart
distinctly offset from the centre of the BoundingBox,
with its leftmost point at approx X=84 points from the left
of the box (at 0), its rightmost point at X=162 approx
54 points from the right of the box (at 216), so the diameter
of the circle is approx 162-84 = 78 points (a bit over 1 inch),
and the centre of the circle is approx at 123 points (X)
which is 15 points to the right of the centre of the box.
Similarly the top of the circle is at approx Y=156 (60 points
from the top of the box) and the bottom is at approx Y=78
from the bottom of the box.

So, although relative dimensions are about right as measured,
the pie-chart is off-centre relative to the BoundingBox,
just as when displayed in the X-window.

I have been able to re-write the %%BoundinBox line by editing
the EPS file until it looks about right, and can then continue.
However, I would like to be able to exactly enclose the pie
chart in the BoundingBox automatically, but the documentation
(in ?pie and in ?postscript) seems to contain nothing that
would give me a clue for achieving this.

By way of background: I want to include the EPS file in a
document where I would use graphics commands to embellish
the pie-chart with my own annotations. For this I need to
be able to calculate the cordinates of points on the chart
relative to its centre; whereas the software will be using
the BoundingBox to locate the imported graphic. So I have
to be able to work out the coordinates of the pie-chart
relative to the BoundingBox. The PostScript code in the EPS
file is difficult to decipher from this point of view, so
(as explained) I have been reduced to editing the Bounding
Box until it looks about right.

Sorry for the long account, but I wanted to try to make the
situation clear.

With thanks for any suggestions!
Ted.

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E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
Fax-to-email: +44 (0)870 094 0861
Date: 10-Mar-10                                       Time: 22:03:41
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