CGAL users discussion list

["Audette, Michel" <>]

Dear All, 

subsequent to the message below, as well as a fruitful discussion with Bernd 
Gaertner, I would like to tweak the algorithm for ellipsoid fitting, so that 
each rounded jaw of a surgical tool sits as a hat over the fitted ellipsoid. 
Currently, the results that we obtain indicates that the algorithm tries to 
center each jaw within an ellipsoidal hull. Is there a simple parameter or 
flag for telling the algorith to perform the fitting in a hat-like manner? 

[Bernd, feel free to respond... I just did not want to take up too much of 
your time...] 

Cheers,

Michel

Michel Audette, Ph.D.  
Innovation Center Computer Assisted Surgery (ICCAS)  
Philipp-Rosenthal-Strasse 55 
Leipzig, Germany 
Phone: ++49 (0) 341 / 97 - 1 20 13 
Fax: ++49 (0) 341 / 97 - 1 20 09 

-----Original Message-----
From: Audette, Michel
Sent: Mon 7/9/2007 10:51 AM
To: 
''
Cc: 'Carina Grühser'
Subject: ellipsoid fitting: incorporating a known or assumed rotation of 
principal axes. 
 
Dear all, 

I have a student who is using CGAL software to perform an ellipsoid fitting 
in order to model the bite of a surgical tool whose mouth opens and closes. 
The fit that we get when the mouth is open appears to be a bad fit, 
unnecessarily large, in part because the ellipsoid seems to want to retain a 
standard orientation of principal axes, when in fact it would be better to 
give the fitting algorithm some other assumed orientation coinciding with the 
plane of symmetry of the open mouth, and a 3rd axis normal to this plane. The 
fitting would be much more compact, and coincide with the actual bite of the 
tool, if we were able to tweak the orientation of principal axes. 

I can send an image of our results, to anyone who responds, to make things 
clearer. 

Is it possible to do this with the CGAL fitting software? Please advise.

Thanks for your kind consideration. 

Best regards, 

Michel Audette, Ph.D.  
Innovation Center Computer Assisted Surgery (ICCAS)  
Philipp-Rosenthal-Strasse 55 
Leipzig, Germany 
Phone: ++49 (0) 341 / 97 - 1 20 13 
Fax: ++49 (0) 341 / 97 - 1 20 09