[Insight-developers] Sanity Check on itkFiniteCylinderSpatialFunction Evaluate

[Williams, Norman K]

I'm investigating this bug report:
https://itk.icts.uiowa.edu/jira/browse/ITK-2576

I suspect that the assumption made by the reporter of this bug is wrong;
for one thing, the one test of this function in ITK doesn't use a cylinder
axis perpendicular to one of the principal axes.

On the other hand, this doesn't make any sense to me either:

  //take square root to normalize the orientation vector
  medialAxisVector[0] = vcl_sqrt(m_Orientation[0]);
  medialAxisVector[1] = vcl_sqrt(m_Orientation[1]);
  medialAxisVector[2] = vcl_sqrt(m_Orientation[2]);

You don't normalize a vector by taking its square root, it should be
something like what the bug report suggests.  I have a patch pushed into
Gerrit that passes existing regression tests:
http://review.source.kitware.com/#/c/8477/


I will hoist the computation of the normalized orientation vector out into
the SetOrientation method tomorrow.

I guess I have this question: Is this comment wrong if I fix this:

  /** Set the orientation vectors (must be orthogonal) of the ellipsoid
axes.
   * Must be normalized!!!!! */
  itkGetConstMacro(Orientation, InputType);
  itkSetMacro(Orientation, InputType);

It seems like the normalized/orthogonal preconditions are unnecessary.

There's also this:
http://www.flipcode.com/archives/Fast_Point-In-Cylinder_Test.shtml

That code has a slightly different definition of a cylinder, but it isn't
a big job to convert between ITK and that code's conventions.



--
Kent Williams norman-k-williams at uiowa.edu






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