Hi itkvtk123<br><br>Thanks for the update.<br><br>* Epsilon will define the convergence criterion<br> So, it effects will not be visible at the beginning <br> of the registration process.<br><br>You may want to play with the following parameters<br>
<br>* InitialRadius<br>* ShrinkFactor<br>* GrowthFactor<br><br>These parameters define the "sphere" around the <br>current parametric point, in which the optimizer <br>will try new values.<br><br>Note that this is done in the parametric space of <br>
the transform, not in physical space.<br><br>The value of InitialRadius, relates to the settings<br>of the parameters scales. For example, if you <br>double all parameter scales values, and you <br>double the InitialRadius, then the optimizer will<br>
behave the same.<br><br>The rule of thum for setting parameter scales<br>is to set rotations to 1.0, so that you can assume<br>that the InitialRadius is set in units of radians <br>(for example : 0.1 radians, which is ~5.7 degrees).<br>
<br>Then you set the translation scales in order to make<br>that a small step of rotation is proportional to a <br>small scale of translation.<br><br>In your case:<br><br> translationscale = 0.1 radian / ( 512 x 1.0 mm)<br>
<br><br>BTW: Is the final rotation of 25 degrees what you were<br>expecting ? This rotation is close to the point of being<br>too large to be solved by registration. You may simply<br>need a better initialization of the Versor transform...<br>
<br><br>Regards,<br><br> Luis<br><br><br>----------------------------------------------------<br><div class="gmail_quote">On Wed, Sep 9, 2009 at 9:42 AM, <span dir="ltr"><<a href="mailto:itkvtk123@gmx.net">itkvtk123@gmx.net</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Hi Luis.<br>
<br>
Thank you for your prompt answer.<br>
I found out that my scales cause the results of 0.<br>
When I comment the scales part, I get results which are different from 0, but which are terribly wrong.<br>
Epsilon does not seem to have much influence in the results, same with the initial transforms.<br>
(It is almost the same (wrong) result when I initialize the initial transforms to 0 or when I use the Initializer).<br>
<br>
In my test case it should detect a X movement of 5, Y movement of 5 and rotation of 5 degrees.<br>
But it actually detects X movement of 10.3, Y movement of -4.4 and rotation of -25.2 degrees.<br>
(By the way X is always wrong in sign regardless which optimizer I use)<br>
<br>
<br>
Is there a rule of thumb for parameters (Epsilon, scales, ...) for 512x512 px (spacing 1mm) images (same modality) when I expect X and Y movement of +- 100 mm each and rotational movement of +- 5 degrees?<br>
<br>
Kind Regards,<br>
itkvtk123<br>
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