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<div>So to the question: "Is this (./Registration/Common/include/itkCenteredVersorTransformInitializer) class useful?" I think the answer is "No".</div>
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<div>I think that the itkLandmarkBasedTransformInitializer.h class does initialize a 3D versor from a set of landmarks. In ITKv4 there is also support for initializing Affine transformations.</div>
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<div>Hans</div>
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<span style="font-weight:bold">From: </span>Bill Lorensen <<a href="mailto:bill.lorensen@gmail.com">bill.lorensen@gmail.com</a>><br>
<span style="font-weight:bold">Date: </span>Sun, 23 Oct 2011 16:35:10 -0400<br>
<span style="font-weight:bold">To: </span>Hans Johnson <<a href="mailto:hans-johnson@uiowa.edu">hans-johnson@uiowa.edu</a>><br>
<span style="font-weight:bold">Cc: </span>Dean Inglis <<a href="mailto:dean.inglis@camris.ca">dean.inglis@camris.ca</a>>, "<a href="mailto:insight-users@itk.org">insight-users@itk.org</a>" <<a href="mailto:insight-users@itk.org">insight-users@itk.org</a>><br>
<span style="font-weight:bold">Subject: </span>Re: [Insight-users] initialize VersorRigid3DTransform<br>
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So how can we help Dean?<br>
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<div class="gmail_quote">On Sun, Oct 23, 2011 at 11:18 AM, Johnson, Hans J <span dir="ltr">
<<a href="mailto:hans-johnson@uiowa.edu">hans-johnson@uiowa.edu</a>></span> wrote:<br>
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<div>Bill,</div>
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<div>In ITKv4 the "Centered" transforms are likely to be deprecated.</div>
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<div>Brian Avants and Luis Ibanez provided the following:</div>
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<ol>
<li>Rationale for removing the CenteredTransforms</li></ol>
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<div style="font-family:Calibri; font-size:medium">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. </div>
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<li>A recommended ITKv4 upgrade path for those using the centered transform</li></ol>
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<div style="font-family:Calibri; font-size:medium">If you were using the centered transforms, we recommend replacing the centered transform with its non-centered equivalent. Then, where one previously wrote:</div>
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<div style="font-family:Calibri; font-size:medium">one would now write </div>
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<div style="font-family:Calibri; font-size:medium">transform->SetFixedParameters(fixed_parameters) </div>
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<div style="font-family:Calibri; font-size:medium">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. </div>
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<div style="font-family:Calibri; font-size:medium">Hans</div>
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<span style="font-weight:bold">From: </span>Bill Lorensen <<a href="mailto:bill.lorensen@gmail.com" target="_blank">bill.lorensen@gmail.com</a>><br>
<span style="font-weight:bold">Date: </span>Sun, 23 Oct 2011 11:11:32 -0400<br>
<span style="font-weight:bold">To: </span>Dean Inglis <<a href="mailto:dean.inglis@camris.ca" target="_blank">dean.inglis@camris.ca</a>><br>
<span style="font-weight:bold">Cc: </span><<a href="mailto:insight-users@itk.org" target="_blank">insight-users@itk.org</a>><br>
<span style="font-weight:bold">Subject: </span>Re: [Insight-users] initialize VersorRigid3DTransform<br>
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<div></div>
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Is this class useful?<br>
./Registration/Common/include/itkCenteredVersorTransformInitializer<br>
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<div class="gmail_quote">On Sat, Oct 22, 2011 at 12:44 PM, Dean Inglis <span dir="ltr">
<<a href="mailto:dean.inglis@camris.ca" target="_blank">dean.inglis@camris.ca</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex; border-left:1px solid rgb(204,204,204); padding-left:1ex">
how can I initialize a VersorRigid3DTransform for a point set<br>
to image registration problem using the following information:<br>
1) center of the moving points, c<br>
2) principal axes of the moving points, e1, e2, e3<br>
3) center of the image calculated using the ImageMomentsCalculator, cofg<br>
4) principal axes of the image calculated using the ImageMomentsCalculator, p1, p2, p3<br>
<br>
where all variables above are double arrays of size 3? Bascally, I would like<br>
to be able to initialize the transform:<br>
ParametersType parameters( transform-><u></u>GetNumberOfParameters() );<br>
<br>
// Versor type<br>
typedef TransformType::VersorType VersorType;<br>
VersorType versor;<br>
<br>
parameters[0] = versor.GetX(); // Rotations<br>
parameters[1] = versor.GetY();<br>
parameters[2] = versor.GetZ();<br>
parameters[3] = 0.0; // Translations<br>
parameters[4] = 0.0;<br>
parameters[5] = 0.0;<br>
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transform->SetParameters( parameters );<br>
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but I dont know how the rotations should be initialized. I could calculate a 3x3 rotation<br>
matrix :<br>
A = e * p<br>
where e = {e1,e2,e3} and p = {p1,p2,p3} but how could that be used to initialize the<br>
transform?<br>
<br>
Dean <br>
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