R help - Jan 2003 - Why are default sizes of plotting characters different?

I had occasion to use panel.superpose to draw points in a lattice
plot, and chose to set the size to 1.1 using trellis.par.set().  I
also wished to add some other plotting characters which I did with
grid.points.  To get them looking like the same size as those done
with panel.superpose, I needed to set the size to 0.8 using size unit(.8,
"char").  Now they end up looking quite similar even if not
identical.

Evidently, the default values have different bases.  What is the
thinking behind those defaults?

thanks



-- 
Patrick Connolly
HortResearch
Mt Albert
Auckland
New Zealand 
Ph: +64-9 815 4200 x 7188
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the beaches of the world ... Perhaps you`ve seen it.  ---Steven Wright 
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On Tuesday 14 January 2003 09:20 pm, Patrick Connolly
wrote:
> I had occasion to use panel.superpose to draw points in a lattice
> plot, and chose to set the size to 1.1 using trellis.par.set().  I
> also wished to add some other plotting characters which I did with
> grid.points.  To get them looking like the same size as those done
> with panel.superpose, I needed to set the size to 0.8 using size >
unit(.8, "char").  Now they end up looking quite similar even if not
> identical.
>
> Evidently, the default values have different bases.  What is the
> thinking behind those defaults?
The grid defaults are whatever Paul decided :) The defaults in lattice were 
chosen so that things look approximately similar to comparable Trellis plots 
in S-Plus. The precise definition in lattice is 

cex = 1 <==> size = unit(2.5, "mm")