[R] Finding the "height of a line of text" for axis
Marc Schwartz
MSchwartz at MedAnalytics.com
Wed Mar 30 16:03:10 CEST 2005
On Wed, 2005-03-30 at 11:06 +0100, Steven J. Murdoch wrote:
> I would like to draw only the ticks of an axis, but not the axis
> itself. I don't think this can be done using axis(), so I am trying to
> write a cut-down version in R, which only draws ticks.
>
> The point at which I am stuck is that the length of a tick is set by
> par("tcl") as a fraction of the "height of a line of text". So I would
> like to draw a line whose length is also this length. However I cannot
> find out how to convert the into units I can pass into lines(). I
> thought par("cxy"), but it is too large, as is shown in the code
> below. Here the red tick marks are longer than the black ones created
> by axis. I have found the relevant function in plot.c:
> "GConvertYUnits(Rf_gpptr(dd)->tcl, LINES, NFC, dd);"
> but can't find the corresponding R function.
>
> Can anyone suggest how to find this out, or solve the problem in a
> different way?
>
> # Inward pointing ticks
> par("tcl"=1)
>
> drawticks <- function(at) {
> # Start of the ticks
> base<-par("usr")[1]
> # Length of the ticks
> l<-par("cxy")[2]*par("tcl")
> for (i in at) {
> lines(c(base,base+l),rep(i,2),col="red")
> }
> }
>
> # Test plot
> plot(c(1,2,3), axes=FALSE)
> # Draw ticks in red
> drawticks(axTicks(2))
> # Overprint with normal axis
> axis(2, axTicks(2))
Steven,
Are you trying to do something like this:
plot(1:5, axes = FALSE)
axis(1, col.axis = "white", tcl = 1)
axis(2, col.axis = "white", tcl = 1)
or perhaps something like this:
plot(1:5, axes = FALSE)
axis(1, col.axis = "white", col = "red", tcl = 1)
axis(1, col.axis = "white", col = "black", tcl = 0)
axis(2, col.axis = "white", col = "red", tcl = 1)
axis(2, col.axis = "white", col = "black", tcl = 0)
or even something like this:
plot(1:5, axes = FALSE)
axis(1, col.axis = "white", col = "red", tcl = 1)
axis(1, col.axis = "white", col = "white", tcl = 0)
axis(2, col.axis = "white", col = "red", tcl = 1)
axis(2, col.axis = "white", col = "white", tcl = 0)
If you do not want the axis labels, use:
plot(1:5, axes = FALSE, ann = FALSE)
HTH,
Marc Schwartz
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