[R] finding contours in a matrix

[Spencer Graves]

A question very much like this was answered two days ago.  I couldn't 
find it from "www.r-project.org" -> search -> R Site Search.  When I 
went "search" -> "searchable mail archives" -> "r-help" -> "date view", 
I found it.  I found two replies with "isocontour-lines" in the subject, 
both dated 6/16/2003.  One referred to the same question having been 
answered in late May.  With that key word, a more targeted search might 
produce more.

hth, spencer graves

Douglas Beare wrote:
> Hi,
> I have matrix of sea bottom depths that I am plotting in R with the function
> 'image'.
> I am particularly interested in the 200m depth contour (I'm using 'distance
> from this feature' as a covariate in a model) and would like to extract the
> data at evenly 
> spaced points along it.  I can easily superimpose a line at 200m using the
> function 'contour'.  What I
> want to know is: can I actually get the data used to plot this line? If I
> just select the relevant data depth[depth==200] I
> get a very few observations, but if I say select depth[depth > 180 & depth <
> 220] I get a "band" of 
> unevenly space data along the contour which I don't want either.
> Regards,
> Doug Beare
> Fisheries Research Services,
> Marine Laboratory,
> Victoria Road,
> Torry,
> Aberdeen, UK.
> Tel. 44 (0) 1224 295314
> 
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