Re: particle analysis-Feret diameter

Posted by Robert Dougherty on Nov 28, 2005; 8:20pm
URL: http://imagej.273.s1.nabble.com/particle-analysis-Feret-diameter-tp3704371p3704383.html

I should clarify that Measure ROI Curve computes the Feret diameter
internally as its starting point, but does not return it.  It returns an
estimate of the length of a curve that follows a centerline of the object.

For the topologists out there, what I think I need to start the calculation
properly for sharply bent objects is a generalization of the Feret diameter
that is something like this:  

Find the longest continuous curve that connects two points of the perimeter
of the ROI and satifies both of the following:

1. The curve must inside the ROI along its entire length.
2. The curve is a minimum-length curve for it endpoints; i.e., it cannot be
shortened by moving its interior points.

I'm visualizing a taught string that connects the endpoints and bends at the
interior kinks of the ROI that it is forced to go around to stay inside the
ROI.  This seems like it must be a standard concept.  Intuitively, this
curve should be unique if the ROI is simply connected.

My plan for updating Measure ROI Curve is to begin with the endpoints for
the above curve (assuming they can be found...) and use the left and right
boundary curves defined by these to find the centerline and its length and
the maximum width using the present algorithm.

Bob

> -----Original Message-----
> From: ImageJ Interest Group [mailto:[hidden email]] On Behalf Of
> Robert Dougherty
> Sent: Monday, November 28, 2005 8:29 AM
> To: [hidden email]
> Subject: Re: particle analysis-Feret diameter
>
> "Measure ROI Curve" on http://www.optinav.com/ImageJplugins/Measure-
> Roi.htm
> can compute the width of a banana, as well as the Feret diameter.  It uses
> an ad-hoc algorithm that works well enough most of the time.
>
> A limitation of Measure ROI Curve has recently been pointed out to me.  If
> the banana is so sharply bent that its interior angle is less than about
> 53
> degrees (where 180 degrees would be a straight banana), then the algorithm
> can get confused.  This happens because the Feret diameter is not what a
> human analyst would regard as the length in this case.  I've been asked to
> address the limitation and have not yet found a solution.
>
> Bob
>
> Robert P. Dougherty, Ph.D.
> President, OptiNav, Inc.
> Phone [phone]
> Fax [phone]
> www.optinav.com
>
> > -----Original Message-----
> > From: ImageJ Interest Group [mailto:[hidden email]] On Behalf Of
> > [hidden email]
> > Sent: Monday, November 28, 2005 5:47 AM
> > To: [hidden email]
> > Subject: Re: particle analysis-Feret diameter
> >
> > Hello,
> > I think that you have only one feret diameter, the maximum.
> > draw the convex hull and then compute all the distances between the
> points
> > in
> > the hull.
> > What is the minimum? The smallest size hole through which the particle
> can
> > pass?
> > How about a banana? Does anybody know of an algorithm that can compute
> the
> > smalles feret for an egg and for a banada?
> > Juist my monday morning thoughts
> > Heberto Ghezzo
> > Meakins-Christie Labs
> > Montreal - canada