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Re: searching for an enveloppe


Olivier Leroy wrote:
> 
> I'd like to know the envelope of a curve. The data come from image
> processing, and are known as a list of points, function of distance.
> Does a method already exist to have an upper envelope near by the curve
> ?
> 
> Juliette Marais
> ___________________
> INRETS
> France.


If your data points are not misbehaving too badly the following approach
might be useful. Assume the curve is approximated by a low degree
polynomial of the form p(x,y)=0.

(i) Find a least-squares fit to obtain coefficients for p(x,y). (ii) Get
an envelope by allowing a small offset, say |p(x,y)|<=epsilon.


Daniel Lichtblau
Wolfram Research


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