R help - Dec 2011 - generalized procrustes analysis without translation

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I?m not aware of any, but if you really want this, it should be possible to
modify the code of any of the functions you propose and delete the part doing
the translation. I?m not sure that this is a good idea, though; either your
matrices are *truly* centered, then it doesn?t make a difference, or they are
only centered in theory but not in practice due to random error, then the
rotation and scaling will depend heavily on the deviation of the center of the
matrix from the origin. Optimal scaling and rotation in GPA are independent from
each other so might be (de-)selected depending on needs, but they depend on the
translation, so it seems to make sense that you cannot deselect that part. You
wouldn?t do scaling of two variables without centering them around 0 either,
would you? You may transform them back if required, but scaling without
centering first does not appeal to me, same for rotations.
HTH, Michael

From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Mark Heckmann
Sent: Wednesday, December 07, 2011 19:09
To: r-help at r-project.org
Subject: [R] generalized procrustes analysis without translation

I am searching for a GPA function/algorithm that allows to omit translation of
matrices.
procGPA in the shapes package does not have this option.
I need scaling, rotation and reflection but no translation as my matrices are
naturally centered.

I am not sure if GPA from FactoMineR might be used for this.
There are no arguments allowing to switch on the above mentioned arguments
except for scaling.
Frankly, I also do not understand how to set up the data for GPA properly,
especially how to use the group argument.

Does someone know another GPA function or has some code available?

Thanks in advance
Mark

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Mark Heckmann
Blog: www.markheckmann.de
R-Blog: http://ryouready.wordpress.com











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