[R] trellis margin sizes in absolute units

[Deepayan Sarkar]

On Thu, Jul 12, 2012 at 9:39 PM, Martin Ivanov <tramni at abv.bg> wrote:
>  Dear R users,
>
> I have a lot of experience with traditional R graphics, but I decided to turn to trellis as
> it was recommended for spatial graphs by the sp package. In traditional R graphics
> I always first set the size of the device region absolute units (e.g.  mm) and then I
> firmly fix the inner margins with mai and the outer margins with oma also in absolute units.
> What is left from the device region is for the plot region. That is my general idea.
>
> My question is, is it possible to achieve that full control with trellis graphics? I have tried
> with the *.paddings parameters, but it seems to me that the margins are still larger than I have set them.
> Here is my example code: (mp is a SpatialPixelsDataFrame)
>
> xlim <- c(.96*bbox(mp)[1, 1], 1.02*bbox(mp)[1, 2]);
> ylim <- c(.992*bbox(mp)[2, 1], 1.005*bbox(mp)[2, 2]);
> b <- 1; t <- 2; # b, t : should be bottom and top figure margins
> l <- 1; r <- 6; # l, r : should be left and right figure margins
> asp <- mapasp(data=mp, xlim=xlim, ylim=ylim);
> # I have set the width of the device region as w millimetres and here I calculate
> # its height, taking care of the aspect ratio
> h <- b + t + asp*(w - (l + r));
>
> postscript(output, onefile=FALSE, paper="special", width=w/25.4, height=h/25.4, horizontal=FALSE, fonts=c("Times"), print.it=FALSE, colormodel="rgb", pointsize=12);
>
> # here I set all the possible paddings to make sure that all other margins are 0:
> trellis.par.set(layout.widths=list(left.padding=l, right.padding=r, key.ylab.padding = 0,
> ylab.axis.padding = 0, axis.key.padding = 0, units="mm"),
> layout.heights=list(bottom.padding=b, top.padding=t, main.key.padding = 0, key.axis.padding = 0, axis.xlab.padding = 0,
> xlab.key.padding = 0, key.sub.padding = 0, units="mm"),
> axis.components=list(bottom=list(pad1=.8), left=list(pad1=.8)));
>
> But still, the resulting margins are larger than I expect and to achieve the desired effect I have to set some parameters to negative numbers. So I guess there are some other graphical parameters that come into play, about which I do not know.
> Which margins are these *.padding parameters controlling: the outer (device) or the inner (figure) margins?

The 'par.settings' are only multipliers for the defaults, and you want
to change the original defaults. For example, the left margin is given
by

> lattice.getOption("layout.widths")$left.padding
$x
[1] 0.5

$units
[1] "char"

which you want to change to, say, list(x = 1, units = "mm"). See
?lattice.options on how to do that (and also the 'lattice.options'
entry in ?xyplot).

You might have better luck with the development version at

https://r-forge.r-project.org/R/?group_id=638

as it has some related bugfixes and documentation improvements.

-Deepayan