Re: [R] "lwd" gives different plotted line widths for Vertical and horizontal Lines when lwd= 2?

From: hadley wickham <h.wickham_at_gmail.com>
Date: Mon, 07 Jul 2008 11:40:22 -0500

Hi Pedro,

Hmm, that's probably a bug in the way that ggplot2 is drawing the lines. The good news is that the next version of ggplot has a much more flexible theming system, so to get the same effect as your grid code, all you'll need to do is:

theme_set(axis.line = theme_segment(colour = "black") theme_set(axis.ticks = theme_segment(colour = "black", size = 3)

I'm still fixing a lot of bugs in the new code (and documenting how it all works), but I hope to have another release out in the near future.

Hadley

On Sun, Jul 6, 2008 at 10:06 AM, Pedro de Barros <pbarros_at_ualg.pt> wrote:
> Hi Hadley,
>
> Thanks for the quick and informative reply.
>
> I did what you suggested, and it was indeed the problem for the axes lines
> (both are the same thickness). However, ticks are still thicker... I am
> attaching the two pdf files (one with lwd=2, the other with lwd=3).
>
> Thanks again,
> Pedro
> At 15:02 2008/07/06, you wrote:
>>
>> On Sun, Jul 6, 2008 at 6:33 AM, Pedro de Barros <pbarros_at_ualg.pt> wrote:
>> > Dear All,
>> >
>> > I have been trying to add lines to the axis grobs of plots produced with
>> > ggplot2.
>> >
>> > The code I have used is below. It works, although I do not think it is a
>> > really elegant way of doing what I want....
>> > However, I am now noticing that when plotted, the width of the lines in
>> > the
>> > axis are not the same as the line widths I get for the ticks (the ticks
>> > get
>> > thicker lines). Also, when I build a function to do the same
>> > conversion, I
>> > get different (thinner) line widths for the x-axis I have been trying to
>> > find out why this is so, but I seem to have met a dead-end.
>> >
>> > #Test
>> > library(ggplot2)
>> > #Set the basic overall plot options
>> > themePublish <-list(background.fill='white', grid.fill='white',
>> > grid.colour='NA', grid.minor.colour='NA', axis.colour='black',
>> > border.colour='NA')
>> > ggtheme(themePublish)
>> >
>> > #Generate the data
>> > plotdata<-data.frame(x=1:10, y=runif(10))
>> >
>> > #Build the ggplot object
>> >
>> > ggPlotObject<-ggplot()
>> > ggPlotObject<-ggPlotObject+layer(data=plotdata,
>> > mapping=aes_string(x='x',y='y'),geom='point', stat='identity', size=4)
>> > ggPlotObject<-ggPlotObject+ scale_y_continuous(limits=c(0,1),
>> > expand=c(0,0))
>> >
>> > #################
>> > #I define the following function
>> > F.ggPlot.AddAxisLines<-function(ggPlotObject, col='black', lwd=2,
>> > lty='solid'){
>> >
>> > ###################################################################################################
>> > # First, capture the ggPlot object as a gTree
>> > ggPlotTree<-ggplot_plot(ggPlotObject)
>> >
>> > #Get the parameters defined for the lines
>> > LinePars <- gpar(col=col, lwd=lwd, lty=lty)
>> >
>> > #Then, create the objects to add to the axes
>> > YAxis.Line<-linesGrob(x=unit(c(1,1), 'npc'), y=unit(c(0,1), 'npc'),
>> > vp='left_axis', name='YAxisLine', gp=LinePars)
>> > XAxis.Line<-linesGrob(x=unit(c(0,1), 'npc'), y=unit(c(1,1), 'npc'),
>> > vp='bottom_axis', name='XAxisLine', gp=LinePars)
>> >
>> > #Add the grobs to this object
>> > ggPlotTreeMod<-ggPlotTree
>> > ggPlotTreeMod<-addGrob(ggPlotTreeMod, YAxis.Line, gPath('yaxis'),
>> > grep=TRUE)
>> > ggPlotTreeMod<-addGrob(ggPlotTreeMod, XAxis.Line, gPath('xaxis'),
>> > grep=TRUE)
>> >
>> > #Edit the properties of the ticks, to match those of the lines
>> > ggPlotTreeMod<-editGrob(ggPlotTreeMod, gPath('ticks'), gp=LinePars,
>> > grep=TRUE, global=TRUE)
>> >
>> > #Output the new object
>> >
>> > ggPlotTreeMod
>> > }
>> >
>> > # and then do
>> > ggPlotTreeMod2 <- F.ggPlot.AddAxisLines(ggPlotObject)
>> > grid.draw(ggPlotTreeMod2)
>> >
>> > # I get different line thicknesses for the two axes
>> >
>> > #However, if I do
>> > ggPlotTreeMod3 <- F.ggPlot.AddAxisLines(ggPlotObject, lwd=3)
>> > grid.draw(ggPlotTreeMod3)
>> >
>> > # I get the same line thickness on both axes, but thicker ticks
>>
>> How are you judging thickness? It may be that due to the size of
>> ticks and the size of the plot surface that thickness of the line is
>> not a whole number of pixels, and depending on the exact position of
>> the line, gets rounded up or down. Trying saving as pdf and zooming
>> in.
>>
>> Hadley
>>
>> --
>> http://had.co.nz/
>

-- 
http://had.co.nz/

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