surface models

• Let S(a) be a surface in 3-D which depends upon a some parameters a.
  
  
• Among these parameters, we distinguish those that affect
  the pose "p" of the surface from the ones that affect its shape "s"
  
  a = (s,p) , so that S(s,p) = p . S(s,0) = p . S(s)
  

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• Problems:
  • Choice of the model class
  • Choice of the model order
  • How can we impose a model on shape without imposing a model on pose and motion?