R help - Feb 2011 - Relationships between png resolution, axis.text$cex trellis setting, and paddings

Dear R-users,

I was wondering if somebody could shed some light on the relationships
existing between the resolution of a png device, the axis.text$cex trellis
setting, and the paddings of the actual graph. In the following code, I
create a custom trellis theme that set (among other thing) axis.text$cex to
1 instead of the default 0.8. Then a lattice graph is created and exported
to three png devices using three different resolutions. You should notice
that the spacing between the axis labels and tick labels decreases at high
resolution. This is not the case if axis.text$cex is kept at 0.8. I have
tried to scale various trellis settings related to padding but that did not
seem to help.

Any idea on how to compensate the change in axis.text$cex would be welcome.

Sebastien



require(lattice)

my.theme <- function() {

  cur.settings <- standard.theme()

  theme <- list(
                background=list(col='transparent'),
                layout.widths=list(left.padding=0.5,
                                   ylab.axis.padding=0,
                                   right.padding=0),
                layout.heights=list(top.padding      =0,
                                    main.key.padding =0,
                                    axis.xlab.padding=0,
                                    key.sub.padding  =0,
                                    bottom.padding   =0.5),
                axis.text=list(cex=1),
                axis.components=list(top=list(tck=0,
                                              pad1=0,
                                              pad2=0),
                                     right=list(tck=0,
                                                pad1=0,
                                                pad2=0)))

  inter.theme <- modifyList(cur.settings, theme)

  return(inter.theme)


}

df <- data.frame(x=-10:10,y=rnorm(21))
myplot <- xyplot(y~x,data=df,
                 xlab="Whatever",ylab="Random")

png(file='padding_test_normal_125.png',
    width=750,
    height=750,
    res=125)

trellis.par.set(my.theme())

print(myplot, split=c(1,1,2,2), more=TRUE,newpage=TRUE)
print(myplot, split=c(1,2,2,2), more=TRUE,newpage=FALSE)
print(myplot, split=c(2,1,2,2), more=TRUE,newpage=FALSE)
print(myplot, split=c(2,2,2,2), more=FALSE,newpage=FALSE)

dev.off()

png(file='padding_test_normal_150.png',
    width=900,
    height=900,
    res=150)

trellis.par.set(my.theme())

print(myplot, split=c(1,1,2,2), more=TRUE,newpage=TRUE)
print(myplot, split=c(1,2,2,2), more=TRUE,newpage=FALSE)
print(myplot, split=c(2,1,2,2), more=TRUE,newpage=FALSE)
print(myplot, split=c(2,2,2,2), more=FALSE,newpage=FALSE)

dev.off()

png(file='padding_test_normal_300.png',
    width=1800,
    height=1800,
    res=300)

trellis.par.set(my.theme())

print(myplot, split=c(1,1,2,2), more=TRUE,newpage=TRUE)
print(myplot, split=c(1,2,2,2), more=TRUE,newpage=FALSE)
print(myplot, split=c(2,1,2,2), more=TRUE,newpage=FALSE)
print(myplot, split=c(2,2,2,2), more=FALSE,newpage=FALSE)

dev.off()

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