Posted by
Robert Smith on
URL: http://imagej.273.s1.nabble.com/Fiji-Drawing-tools-tp5024409p5024417.html
Please excuse my interruption however may I suggest simply orient the image on your screen, take a screenshot (Plugins > Utilities > Capture image). Then set the Analysis to measure the long and short Feret axis on the image?
Just asking,
Bob
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From: Kenneth R Sloan<mailto:
[hidden email]>
Sent: Wednesday, January 27, 2021 8:49 AM
To:
[hidden email]<mailto:
[hidden email]>
Subject: Re: Longest axis/minimum containing sphere of 3D object?
I agree that this is the right way to characterize “longest axis”.
But... the OP did ask for Diameter, which is not the same thing.
Also, I have always been suspicious of methods that find eigenvectors and
eigenvalues and then multiply by a magic constant. This last step has too
many assumptions about the distribution of input points. My preferred
method is to project the input points on the major axis and scale both axes
so that the major axis matches the maximum extent of the projection.
Consider the difference between a solid object and the points on the
boundary of the object. This (I think) requires different scaling
constants. You must take care to verify that your problem matches the
assumptions baked into the method!
If the OP still wants Diameter, my opinion is that:
A) minimum enclosing circle is not quite correct,
B) I would find the 3D Convex Hull and then use the obvious brute force
method of finding the Diameter
Both of these appear to require code that goes beyond existing “off the
shelf” methods. I suppose that B could be done in the macro language, but
my personal preference would be Java.
The 3D suite can provide a good ESTIMATE of the Diameter, and it is up to
the OP to decide if the estimate is acceptable. This also looks like the
FASTEST method, if that matters.
On Wed, Jan 27, 2021 at 02:56 Straatman, Kees (Dr.) <
[hidden email]>
wrote:
--
-Kenneth Sloan
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