[R] Follow up: surfaces and digital terrain model

Andrew Niccolai andrew.niccolai at yale.edu
Thu May 31 22:54:17 CEST 2007

I realize that as of yesterday, this message thread is 4 years old but can
someone possibly post the clines function that Renaud mentions in the
posting below?  That would be wonderful and most appreciated.


Andrew Niccolai
Doctoral Candidate
Yale School of Forestry

From: Renaud Lancelot <lancelot>
Date: Fri May 30 22:37:02 2003

Yesterday, I posted the following:

>>I have computed a digital terrain model from a set of points (x, y, z)
>>using the function interp() in package akima. I want to predict flooded
>>surfaces given target values of z. I can display the flooded surfaces
>>with contour() or image(), but I don't know how to get the polygons
>>delimiting the surfaces. Did anyone write a function for this purpose ?

Many thanks to Roger Bivand, Paul Murrel, Deepayan Sarkar, Barry
Rowlingson and Thomas W Blackwell for their replies and their help. Paul
Murrel provided me with a function "clines", kindly ported to Windows by
Duncan Murdoch. This function does exactly what I need, i.e. it returns
a list of polygons corresponding to target value(s) of z.

I wrote a function to compute (hopefully !) what I want, i.e. predicted
flooded surfaces given target values of z (managing the cases of several
independent watered surfaces, possibly with islands). Provided that Paul
Murrel agrees to share his function, I will be happy to send it to
anyone wishing to use and improve it (and debug it ;-) ).

Best regards and thanks again,


Dr Renaud Lancelot, v?t?rinaire
CIRAD, D?partement Elevage et M?decine V?t?rinaire (CIRAD-Emvt)
Programme Productions Animales
ISRA-LNERV                      tel    +221 832 49 02
BP 2057 Dakar-Hann              fax    +221 821 18 79 (CIRAD)
Senegal                         e-mail renaud.lancelot_at_cirad.fr

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