Why are the axis labels too large when using tikzDevice and lattice?

Question

I'm working on a paper that is to be submitted to an Elsevier journal. The official guidelines state that:

As a general rule, the lettering on the artwork should have a finished, printed size of 7 pt for normal text and no smaller than 6 pt for subscript and superscript characters.

I use the knitr + lattice + tikzDevice combination. I set the following options:

opts_chunk$set(include=FALSE, error=FALSE, warning=FALSE, echo=FALSE,
dev="tikz", dev.args=list(pointsize=10), fig.align="center")

And my plot is generated with fig.width=3.5, fig.height=3.5. I get the following result with a call to xyplot, without passing any cex option:

The axis labels are larger than the main text, whose normalsize is 10pt (I think---I'm using the elsarticle document class with the 3p option).

When I open one of the generated tikz files, I found several node declarations such as this one:

\node[text=drawColor,anchor=base,inner sep=0pt, outer sep=0pt, scale=  1.20] at (137.00, 12.04) {Day};

It looks like tikzDevice applies a scale factor of 1.2 to the axis labels; strangely, this does not seem to be the case with graphics produced with base graphics.

Any idea why this behaviour, and what I can do to bring the size of axis labels down to the desired 7pt?

Answer 1

Since I posed that question I've switched to ggplot, and with that package I get the size I need by changing the base_size parameter of the theme:

theme_set(theme_bw(base_size = 7))

I haven't checked but I suspect something similar can be done with lattice.

Answer 2

I'm using ggplot too, but setting the base_size as lindelof proposed didn't work for me. What did the trick was explicitly setting the font size for the axis labels:

ggplot(...) + theme(axis.title = element_text(size = 10))