[ITK] [ITK-users] minimize skewing

[Hammond, Emily M]

Thank you for your suggestion. It has been helpful!

I have implemented the ScaleVersor3DTransform and have received results. However, every time the rotation is much larger causing terrible results. Here is an example of a final transform received.

scaleVersorTransform information:
   Rotation: [ -0.606402, 0.792956, 0.0591457, 1.41421e-005 ]
   Translation: [9.16674, -1.28393, -17.1493]
   Scale: [4.08189, 1.52688, 2.35832]

I haven't had much experience with versors, but I went through the calculations from a previous mailing list email (http://public.kitware.com/pipermail/insight-users/2009-March/029584.html) and got a very very large rotation that is occurring (as is seen in the resulting image). Is there any reason that I may be getting such a large, unrealistic rotation?

Here is how I've set up my optimizer:

typedef itk::RegularStepGradientDescentOptimizer GDOptimizerType;
GDOptimizerType::Pointer gdOptimizer = GDOptimizerType::New();

// set up optimizer
gdOptimizer->SetNumberOfIterations( 200 );
gdOptimizer->SetRelaxationFactor( 0.9 );
gdOptimizer->SetMinimumStepLength( 0.001 );
gdOptimizer->SetMaximumStepLength( 5.0 );
gdOptimizer->SetGradientMagnitudeTolerance( 0.001 );

// initialize optimizer scales
typedef GDOptimizerType::ScalesType OptimizerScalesType;
OptimizerScalesType optimizerScales( scaleVersorTransform->GetNumberOfParameters() );
// rotation
const double rotationScale = 1.0/10000.0;
optimizerScales[0] = rotationScale;
optimizerScales[1] = rotationScale;
optimizerScales[2] = rotationScale;
// translation
const double translationScale = 1.0/1000.0;
optimizerScales[3] = translationScale;
optimizerScales[4] = translationScale;
optimizerScales[5] = translationScale;
// scaling
const double scalingScale = 1.0/100.0;
optimizerScales[6] = scalingScale;
optimizerScales[7] = scalingScale;
optimizerScales[8] = scalingScale;
// set scales
gdOptimizer->SetScales( optimizerScales );

Any advice would be great!
Thanks!

Emily Hammond

________________________________
From: Bradley Lowekamp [blowekamp at mail.nih.gov]
Sent: Wednesday, November 19, 2014 12:52 PM
To: Hammond, Emily M
Cc: insight users
Subject: Re: [ITK-users] minimize skewing

Hello,

For 3D you might want to look into the ScaleVersor3DTransform or the ScaleSkewVersor3DTransform. These may parameterize the transform as you wish.

Brad

On Nov 19, 2014, at 11:56 AM, Hammond, Emily M <emily-hammond at uiowa.edu<mailto:emily-hammond at uiowa.edu>> wrote:

Hello all,

I am looking perform registration allowing for translation, rotation and anisotropic scaling. Is there a way to use the affine transform but limit the skewing performed? Or is there an alternative method to do this.

Thanks!
Emily Hammond
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