surfaces and digital terrain model

Dear all,

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 ?

Best regards,

Renaud

Dr Renaud Lancelot, v?t?rinaire
CIRAD, D?partement Elevage et M?decine V?t?rinaire (CIRAD-Emvt)
Programme Productions Animales
http://www.cirad.fr/presentation/programmes/prod-ani.shtml

ISRA-LNERV                      tel    (221) 832 49 02
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Senegal                         e-mail renaud.lancelot at cirad.fr