On 08/18/2010 08:40 PM, David Hajage wrote:
Hello,
I am using mtext to write some text below a graph:
plot(1)
mtext("foo", side = 1, line = 2, at = seq(0.6, 1.6, 0.2))
I would like to draw something near the "foo" texts, for example a segment.
For this, I need to know the coordinates of the text ploted by mtext
function.
I spent a few hours to try different combination, using the option xpd =
TRUE and trying to convert between graphics coordinate system using
grconvertX and grconvertY... But I can't make it.
Is there a way to know the coordinates of the text produce by mtext,
particularly vertical coordinates? For example, how can you draw some
segments to underline each foo in my example?
Hi David,
You can get the "X" coordinates of the beginning and end of the text by
using the strwidth function:
# this is inefficient, but easy to follow
begintext<-at-strwidth("foo")*par("adj")
endtext<-at+strwidth("foo")*(1-par("adj"))
the strheight function can be used to get the "Y" coordinates:
bottomtext<-par("usr")[1]-(line+0.5)*strheight("Ug")
You will probably have to fiddle with the constant (0.5) to get the line
in the correct place on a particular device, then:
par(xpd=TRUE)
segments(begintext,bottomtext,endtext,bottomtext)
par(xpd=FALSE)
Jim
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