[R] finding contours in a matrix

[Roger D. Peng]

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-roger

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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