[Insight-users] Best optimizer for landmark registration with only 3 points

[Alireza Salamy]

Hi Charlotte
   
  If you only have Three points, you could rather use the class:

         itkLandmarkBasedTransformInitializer


if you do not have the correspondence between the points, well...
this methods is so fast with only Three points that you could
actually try all the combinations and settle for the one with
the smallest final squared errors,otherwise your own suggestion of duplicating the landmarks should work.
   
  I hope it works.
  Alireza

Charlotte Curtis <curtisc at uoguelph.ca> wrote:
  I'd like to use landmark registration to get a rough first guess prior to image registration.  When I run IterativeClosestPoint2 with 4 landmarks, it complains about the number of landmarks:

vnl_least_squares_function: WARNING: unknowns(6) > residuals(4) 
vnl_levenberg_marquardt: Number of unknowns(6) greater than number of data (4)
Solution = [0, 0, 0, 0, 0, 0]

I'm just wondering if there's an optimizer that would let me get away with a minimum of three landmarks.  Since 3 points would define a unique location in 3D space, it seems to me that there shouldn't need to be 6.  Indeed, if I simply duplicate all of my landmarks and fool it into thinking it has 8 unique points, it comes up with a reasonable solution.  This is my backup plan if nothing else works, but it seems a little messy.  Any suggestions?  Thanks, 

Charlotte _______________________________________________
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