Define plot elements size in mm (R)

Question

I am preparing figures in R for submission to a journal. Required formatting is given in mm (line width = 0.5mm, symbols = 3mm, etc).

I know how to define the figure size in mm, and to manage line width and symbol size with respectively lwd and cex, either in par() or within the plot function. I also found how to convert points to mm. However I don't know how to define line weight, text size, etc. precisely, and not "scaling up" as usual (eg. I want lwd = 0.5mm, not lwd = 1.2 x the default size).

I hope I am clear enough =)

Here is my code :

jpeg(paste('path-to-figure.jpg'), width=15, height=7)

plot(x, y, main = 'TITLE', xlab = "X NAME",ylab = 'Y NAME', ylim = c(0,180), xlim = c(0, 4)pch = 1)

dev.off()

Many Thanks !

Answer 1

Line widths in the standard jpeg, png etc. graphics devices are defined in 1/96 of an inch. See https://stat.ethz.ch/R-manual/R-devel/library/grDevices/html/png.html . The same is true for pdf but may vary for other devices. 0.5 mm = 0.5 / 25.4 * 96 = 1.890 96ths of an inch. So you would use lwd = 1.89.

You could also consider using ggplot2 since size within that is in mm anyway.

E.g.

ggplot(my_data, aes(x, y)) + geom_line(size = 0.5)