[R] contour(): lines & labels in different colours?

[Duncan Murdoch]

On 22/11/2009 5:21 PM, David Winsemius wrote:
> On Nov 22, 2009, at 4:57 PM, Peter Ehlers wrote:
> 
>> Hi Ted,
>>
>> This won't solve your problem, but a small improvement might
>> be to place the labels over the lines rather than the other
>> way around. It will definitely avoid putting red lines over
>> black ones:
>>
>> x <- -6:16
>> z <- outer(x,x)
>> contour(z, labels="", col=2)
>> contour(z, lty=0, labcex=1, add=TRUE)
> 
> I played around a bit with you example, and can get almost the desired  
> color and lack of cutting through labels. There is the possibility of  
> plotting empty labels that create a space in the curves for the later  
> labels-without-lines overlay:
> 
> x <- -6:16
> z <- outer(x,x)
> contour(z, labels="    ", col=2, labcex=1.5, drawlabels=TRUE)
> contour(z, lty=0, labcex=1.5, add=TRUE)

That's a nice solution.  You could probably do a bit better in a couple 
of steps:  1st, figure out what the level labels will be (by default, 
pretty(range(z, finite=TRUE), 10) ), then compute an equivalent number 
of spaces, e.g.

levels <- pretty(range(z, finite=TRUE), 10)
strwidth(levels, cex=1.5) / strwidth(" ", cex=0.5)

Then use the appropriate number of spaces as the labels in the first 
plot, and the numbers in the second one.  Do we have a simple function 
to take input like c(10, 12) and produce two character strings 
containing 10 and 12 spaces?

Duncan Murdoch

> 
> 
>> Cheers,
>> Peter
>>
>>
>> (Ted Harding) wrote:
>>> Greetings, All!
>>> I want to draw contour lines in red, using contour(), but also
>>> have the contour labels (for the level-values) in black so that
>>> they will stand out against a coloured background already generated
>>> using filled.contour() (the background shades from green at low
>>> levels of "risk" to red at high levels).
>>> In any case, contour labels in red are already somewhat inconspicuous
>>> with contour lines in red, regardless of background.
>>> I see nothing in ?contour nor in ?par about this.
>>> One way to approach it could be to first draw the labelled contours
>>> in black, and then overlay by re-drawing (with out labels) in red.
>>> This would sort-of work, but the red contour lines would then cut
>>> through the black numbers, which is somewhat undesirable. Also
>>> (I've tried it) you can get show-through along the contour lines
>>> from the black layer, which is nasty.
>>> Any suggestions?
>>> With thanks,
>>> Ted.
>>> --------------------------------------------------------------------
>>> E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
>>> Fax-to-email: +44 (0)870 094 0861
>>> Date: 22-Nov-09                                       Time: 17:06:08
>>> ------------------------------ XFMail ------------------------------
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>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
> 
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.