Sorry, Brad, but I'm currently in Salt Lake at a funeral. I'd really like to understand better so, if you're available, I can do it anytime during the week on another call.
Sent from Howling Fantods > On Aug 1, 2014, at 7:36 AM, Bradley Lowekamp <[email protected]> wrote: > > Nick, > > I hope you can make it to today's TCON. I can demo that notebook I linked > too. It should clarify things. > > Brad > > On Jul 30, 2014, at 1:57 PM, Nicholas Tustison <[email protected]> wrote: > >>> To try to summaries... sorry if have not been clear enough in my >>> explanations. >> >> No, I blame me—I’m consistently distracted by the scenery outside here in >> California and it’s definitely affecting my ability to concentrate on code >> questions. >> >>> INITIAL QUESTION >>> >>> How does composite transform and the "Center" parameter interact? How does >>> this relate to the virtual domain? >> >> The composite transform is agnostic with respect to whether or not a >> transform has a center or any other fixed parameter set. The only >> distinction we make is typology with respect to linear/deformable. To >> be clear, we’re not discussing any of the “Centered” transforms: >> >> * CenteredAffineTransform >> * CenteredEuler3DTransform >> * CenteredEuler2DTransform >> * CenteredSimilarity2DTransform >> >> None of those transforms are used in ANTs but I don’t think >> their optimization would be an issue in the new ITKv4 registration >> framework. >> >> The virtual domain is simply defined in terms of standard image >> geometry (origin, spacing, etc.) and is currently set in terms of the >> fixed image geometry. >> >>> MY UNDERSTANDING >>> >>> 1) Using a "Center" initialized transform only works correctly for a single >>> transform and directly with a composite. ( This is with the current center >>> initializers, a different approach could be done which takes into >>> consideration the composition ) >> >> I don’t see why it would only work correctly for a single transform. Suppose >> I optimize a translation transform to get it’s optimal parameters for a given >> registration problem. It’s not clear to me why it would be a problem to >> follow >> that with optimizing an Euler3D transform (which we do all the time in >> ANTs). >> Obviously, we have to specify a staring point for the second transform (which >> is identity by default) and perhaps it would be better to have a different >> starting point but I don’t see why starting with the default parameters is a >> problem. >> >> If the “Center initialized transform” is one of the transforms listed above >> then we don’t use those. If it’s simply the result of using the >> CenteredTransformInitializer, then we just pull the >> itk::TranslationTransform >> part from the result and push that translation transform into the composite >> transform queue. I don’t see why it would be a problem to then optimize, >> for example, the Euler3DTransform which just has 3 translation parameters >> and 3 angle parameters to optimize where the center is implicitly defined >> (unlike the CenteredEuler3DTransform which does have additional Center >> parameters). >> >>> 2) The virtual domain should be initialized such that the two images >>> "Center"s are at the origin. This an alternative to using the "Center" >>> transform parameters, and better works with composite transforms. >> >> Yes, that would probably be a better initialization but I don’t know why it >> would >> be a problem for the current framework to optimize with the origin elsewhere. >> Right now, each transform within the composite transform queue is >> optimized starting from its identity parameters but perhaps the initializer >> idea that you propose would improve optimization. >> >>> I was not aware that 2 was the best practice with the ITKv4 framework. Do >>> we have any examples/test/documentation to indicate this? Further more >>> using the current CenterTransformInitalizers to initialize the virtual >>> domain is not readily apparent[1] how to map the parameters. >>> PROPOSAL >>> >>> Perhaps we need a new Initializer filter to assist with initializing the >>> virtual domain to initialize this practice? >>> >>> Brad > _______________________________________________ Powered by www.kitware.com Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html Kitware offers ITK Training Courses, for more information visit: http://kitware.com/products/protraining.php Please keep messages on-topic and check the ITK FAQ at: http://www.itk.org/Wiki/ITK_FAQ Follow this link to subscribe/unsubscribe: http://public.kitware.com/mailman/listinfo/insight-developers
