| Re: Iso-contours at maximum/minimum levels [message #64950 is a reply to message #64891] |
Mon, 02 February 2009 11:00   |
pgrigis
Messages: 436
Registered: September 2007
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Senior Member |
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I sent a method last week that will do that
without derivatives. Have you tried it?
It works very well for me.
Ciao,
Paolo
David Fanning wrote:
> Gianluca Li Causi writes:
>
>> I thanks you for the interesting discussione and I agree with David
>> that the word "contour" means a line that "encloses something", but
>> still you've not given indications for a working "imprint" function,
>> which is what I need.
>>
>> The best that I've found, when the function derivatives are
>> continuous, is to make the contour at level=0 of the partial
>> derivatives dz/dx and dz/dy, which effectively produce a nice
>> "imprint" line BUT also contains some extra lines, corresponding to
>> where one derivative is null but the other is not.
>>
>> So one could take both the zero contours of the two derivatives and
>> say that the "imprint" line is the common curve among these two
>> contours (don't really know how to do this in practice).
>>
>> In any case this does not work with not continuous derivatives, like
>> my first example.
>>
>> How could I search if such an "imprint" function is available anywhere
>> in the IDL library of somebody? Is there an IDL libraries database
>> somewhere in the internet?
>
> I tried this, and I at least get a circle:
>
> IDL> TVScale, Sobel(z), /KEEP
>
> I think something like that might work, with perhaps some thresholding,
> etc.
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Coyote's Guide to IDL Programming (www.dfanning.com)
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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