[Insight-users] initialize VersorRigid3DTransform

[Bill Lorensen]

So how can we help Dean?

On Sun, Oct 23, 2011 at 11:18 AM, Johnson, Hans J <hans-johnson at uiowa.edu>wrote:

>  Bill,
>
>  In ITKv4 the "Centered" transforms are likely to be deprecated.
>
>  Brian Avants and Luis Ibanez provided the following:
>
>
>>    1. Rationale for removing the CenteredTransforms
>>
>>
>  The goal of the centered transforms was to attempt to optimize both the
> center of rotation and the transform parameters.  This leads to a poorly
> posed optimization problem because, as one changes the center of rotation,
> the optimization landscape also changes leading to unstable performance.
>
>
>>
>>    1. A recommended ITKv4 upgrade path for those using the centered
>>    transform
>>
>>
>  If you were using the centered transforms, we recommend replacing the
> centered transform with its non-centered equivalent.  Then, where one
> previously wrote:
>
>  transform->SetCenter(center)
>
>  one would now write
>
>  transform->SetFixedParameters(fixed_parameters)
>
>  where the fixed_parameters will depend on which transform is being used.
>   For matrix transforms, this will be the center of rotation (check this)
> and may be equal to the image's origin.    For dense mappings ( BSpline,
> displacement fields )  , this will be the image spacing, direction, origin.
>
>
>
>
>  Hans
>
>
>   From: Bill Lorensen <bill.lorensen at gmail.com>
> Date: Sun, 23 Oct 2011 11:11:32 -0400
> To: Dean Inglis <dean.inglis at camris.ca>
> Cc: <insight-users at itk.org>
> Subject: Re: [Insight-users] initialize VersorRigid3DTransform
>
>  Is this class useful?
> ./Registration/Common/include/itkCenteredVersorTransformInitializer
>
>
> On Sat, Oct 22, 2011 at 12:44 PM, Dean Inglis <dean.inglis at camris.ca>wrote:
>
>> how can I initialize a VersorRigid3DTransform for a point set
>> to image registration problem using the following information:
>> 1) center of the moving points, c
>> 2) principal axes of the moving points, e1, e2, e3
>> 3) center of the image calculated using the ImageMomentsCalculator, cofg
>> 4) principal axes of the image calculated using the
>> ImageMomentsCalculator, p1, p2, p3
>>
>> where all variables above are double arrays of size 3?  Bascally, I would
>> like
>> to be able to initialize the transform:
>>   ParametersType parameters( transform->**GetNumberOfParameters() );
>>
>>  //  Versor type
>>   typedef    TransformType::VersorType      VersorType;
>>   VersorType versor;
>>
>>   parameters[0] = versor.GetX();   // Rotations
>>   parameters[1] = versor.GetY();
>>   parameters[2] = versor.GetZ();
>>   parameters[3] = 0.0;             // Translations
>>   parameters[4] = 0.0;
>>   parameters[5] = 0.0;
>>
>>
>>   transform->SetParameters( parameters );
>>
>> but I dont know how the rotations should be initialized.  I could
>> calculate a 3x3 rotation
>> matrix :
>> A = e * p
>> where e = {e1,e2,e3} and p = {p1,p2,p3} but how could that be used to
>> initialize the
>> transform?
>>
>> Dean
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