[Insight-developers] Scales estimation for registration

[Bill Lorensen]

Marius, Stefan and Bao,

One of the major weaknesses in ITK's registration framework is the
estimation of parameters. In particular, the estimation of the scales
seems to require special magic. My experience has been that the
selection of a proper scaling for translation is particularly
difficult. ITK traditionally (and currently) leaves the scaling
decision up to the application. There are currently two possible
approaches to this estimation.

1) Bao's itkParameterScaleEstimator proposed in this gerrit topic:
   http://review.source.kitware.com/#change,1499
2) Elastix's (http://elastix.isi.uu.nl/) AutomaticScalesEstimation
   method implementation in elxTransformBase.

For Marius and Stefan I have questions:

a) How successful is elastix's AutomaticScalesEstimation?
b) Currently this is implemented as a method in
   elxTransformBase. Could it be implemented in an API similar to Bao's
   itkParameterScaleEstimator?


For Bao's implementation, my concern is the addition of a free
parameter GlobalScalingFactor. It is not clear how to pick a proper
value. To me there is as much mystery in this parameter as there is in
picking a proper translation scaling

Bill
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