[vtkusers] Angle between two vectors

[Harold]

Thanks David. That reduces the number of calculation.So I guess there isn't any vtk method I can call to get the angle.

Harold 



On Friday, January 3, 2014 11:52 PM, David Cole <dlrdave at aol.com> wrote:
 
Your "get_angle_new" is about as simple as it gets.

I would do something like this, though:

    double dot = vtkMath::Dot(v1, v2);

     // Expect v1 and v2 to be normalized unit vectors, but sometimes 
the dot product
    // exceeds 1 by just enough to cause errors when calling acos.
    // If it's greater than 1.0, or less than -1.0, clamp it:
    if (dot > 1.0)
      {
      dot = 1.0;
      }
    else if (dot < -1.0)
      {
      dot = -1.0;
      }

    double angle = acos(dot);


HTH,
David C.
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