[vtkusers] vtkProcrustesAlignmentFilter problem

[Jonathan.Bailleul]

> Sebastián Ordás wrote:
> 
> Hi,
> I have a doubt regarding the vtkProcrustesAlignmentFilter
> functionality. I have two sets of vtkPolyDatas which come from
> a triangulation on the same object, but having a different number of
> points. If I align each set as RigidBody
> I get the same mean shapes (with GetMeanPoints()) , but when using the
> Similarity option I get two mean shapes of different size. Is it
> correct to expect getting mean shapes of the same size? If not, how
> can I estimate the corresponding scaling factor?
> Thanks in advance.
> 
> Best,
> Sebastian


Dear Sebastian, (sorry for duplicate mail)

The Procrustes Algorithms works with the assumption that all shapes have
the same number of points. More than that, it expects that each point is
implicitely "numbered" in order of appearance, designating the same
anatomical locus (i.e point 0 will designate the tip of the index in
every hand, if you have a tset of hands). Alignment will be performed so
as to minimize a squared sum of distances between points of same number.

So, if you just want to align meshed without correspondence and with
variable point cardinality, consider using ICP instead (should make the
trick).

Best regards,

-- 
-----------------------------------
Jonathan BAILLEUL, Doctorant
GREYC Image - Université de Caen 
http://www.greyc.ismra.fr/~bailleul