R help - Oct 2008 - Best way of figuring out whether graphical elements overlap?

Hi all,

I'm plotting impulses, where some of them should have labels hovering above
them. I know of plotrix' spread.labels function, but would like to save that
for instances where there truely is to little space for the label.
Does anybody have any hints what' the most efficient way might be to achieve
the following:
- plot an impulse plot
- before placing each of a vector of text labels, check (using strhight/width),
whether this collides graphically with anything already plotted and only plot it
if not.

Thanks for any hints, Joh

There is also the spread.labs function in the TeachingDemos package that uses a
different method from the plotrix function and should not move any labels that
are not overlapping.  There are also the dynIdentify and TkIdentify functions in
the same package that allow you to interactively move labels around to where you
are happy with their positions, then returns the coordinates to use for the
positions in a final version of the plot.

If you want to check by hand, you can use the strheight and strwidth functions
to find the bounding rectangles and see if they overlap (there can be some cases
where the actual text does not overlap even if the rectangles do).

Hope this helps,

--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Johannes Graumann
> Sent: Tuesday, October 28, 2008 8:42 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Best way of figuring out whether graphical elements
> overlap?
>
> Hi all,
>
> I'm plotting impulses, where some of them should have labels hovering
> above them. I know of plotrix' spread.labels function, but would like
> to save that for instances where there truely is to little space for
> the label.
> Does anybody have any hints what' the most efficient way might be to
> achieve the following:
> - plot an impulse plot
> - before placing each of a vector of text labels, check (using
> strhight/width), whether this collides graphically with anything
> already plotted and only plot it if not.
>
> Thanks for any hints, Joh
>
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