Re: particle analysis-Feret diameter

Posted by Gabriel Landini on Nov 27, 2005; 5:01pm
URL: http://imagej.273.s1.nabble.com/particle-analysis-Feret-diameter-tp3704371p3704388.html

On Sun, 27 Nov 2005, Kyriakos Kachrimanis wrote:

> > How do you propose to place the other feret diameters at n angles?
> > Is this based on the image frame of reference or angles offset from the
> > direction of the largest one?
> > And what should one use, the centroid or the centre of mass of the particle?
> > Note that when using the centre of mass, holes in the particle make it
> > difficult to standardise the measurements (the same particle filled and with
> > holes has different feret legths because the "centre" is in a different
> > location.
>
> Feret diameter is affected by particle orientation and the only way to
> minimize
> variations due to particle orientation is to measure it at many different
> angles. It doesn't matter how you rotate the particle, the dependency on
> initial orientation will not go away completely. But the variation will be
> minimal if many angles are used. Typically, commercial systems use from 32 to
> sometimes more 72 angles, but usually 72 are sufficient.

Hi,

The maximum feret diameter calculated with the method described in
my previous message is independent on the particle orientation. But
perhaps I am missing something.


Is the definition you are using the maximun difference in (let's say) the
x direction, then rotate the particle and find again this difference, and
measure the length of the particle in the same x directions and so on?
This would mean that the same particle if analysed by 2 people
using a different number of rotations would possibly give different
results.
Furthermore, I suspect that the true particle longest diameter cannot be
guaranteed to be found this way either?

Cheers,

Gabriel