Re: Roundness calculation

Posted by Gabriel Landini on
URL: http://imagej.273.s1.nabble.com/Roundness-calculation-tp5003742p5003745.html

On Tuesday 02 Jul 2013 21:32:18 Heeschen, Bill  wrote:

> The problem with using MajorAxis is that it is a secondary measurement
> derived using the algorithm that fits an ellipse to an object (which I use
> heavily, by the way.)  In order to mathematically explain ImageJ's
> Roundness calculation, one must also explain the ellipse-fitting
> calculation and then explain why it is the best choice for generating the
> value to describe Roundness.  The problem, of course, is that the
> ellipse-fitting calculation coerces the numeric description of the object
> (major/minor axes) toward something that is nominally round by assuming
> that the object can be approximated by an ellipse!
>
> Having now implied that Feret is the more-robust number, there are
> pathologic cases - such as an equilateral triangle - where even the Feret
> is a poor estimation of the minimum circumscribed circle!

Hi,
I had a look in Russ' book and he mentions the maximum diameter.

http://books.google.co.uk/books?id=gxXXRJWfEsoC&pg=PA600&lpg=PA600&vq=roundness

Particles8 uses the Feret diameter but in the end, I think whichever
definition you choose is fine if you are explicit about the algorithm so
others can repeat the measurement.

Cheers

Gabriel

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