AIMS shape moment on disconnected objects in same volume

AIMS library and commands usage

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shishir
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AIMS shape moment on disconnected objects in same volume

Postby shishir » Tue Jun 05, 2007 7:51 pm

Hi Dr. Mangin,

I wanted to ask you a fairly basic question about your BrainVisa program, more specifically with the AIMS shape moment command. If you have a binary volume of 3 disconnected objects (with the same label), how does aims/vip calculate the moment features? Does it calculate each object separately and then find the shape moments/moment invariants and subsequently averages it to output one table of features? Is there a way to calculate the shape properties separately without changing the label for each of the 3 disconnected objects?

Also, in your brain morphometry analysis with 3D shape moments you only took into consideration the invariant moment features...not the other shape moment features (i.e. nu2xy, etc) right? And the reasoning was that the other shape moment features would have a large degree of variation for a same object that was had been modified via translation/rotation?


Thanks again,

Shishir

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riviere
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Postby riviere » Fri Jun 08, 2007 10:37 pm

Hi,
Which program are you talking about ? the AimsMoment command, or is there anything in brainvisa ?
For disconnected objects both behaviours are possible, but we normally calculate moments on the union of all parts to have a homogen set of features even if objects you are comparing have different numbers of connected components.
We look at invariant moments to try to study 'pure shape' descriptors and see if there is anything significant in it. Position, size and orientation are extracted separately, and so the moment features are not correlated to them. Moreover position, size and orientation might be correlated to global effects (size of the subject, or even registration errors) so the invariant moments are 'cleaned' of these potential correlations.
Denis

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Jean-Francois Mangin
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Postby Jean-Francois Mangin » Mon Jun 11, 2007 12:45 am

If you labelled the different objects differently, I think you can select the object you want to compute the invariant for. I am traveling this week, I can not tell you more. Furthermore, the guy who coded all this stuff is Fabrice Poupon, hope he will tell you more...

You are right, we do not use the nu stuff


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