STYLE: Simplify local variable compuations

Provide simpler code to more closely match the mathematical description
of computations that are occuring.

Remove unnecessary "if" statement that is very rarely used,
and is never required for correct computation.

Modules/Core/Transform/include/itkVersorRigid3DTransform.hxx

@@ -56,19 +56,14 @@ VersorRigid3DTransform<TParametersValueType>::SetParameters(const ParametersType
   // Transfer the versor part
 
   AxisType axis;
-
-  double norm = parameters[0] * parameters[0];
   axis[0] = parameters[0];
-  norm += parameters[1] * parameters[1];
   axis[1] = parameters[1];
-  norm += parameters[2] * parameters[2];
   axis[2] = parameters[2];
-  if (norm > 0)
-  {
-    norm = std::sqrt(norm);
-  }
 
-  double epsilon = 1e-10;
+  const double norm =
+    std::sqrt(parameters[0] * parameters[0] + parameters[1] * parameters[1] + parameters[2] * parameters[2]);
+
+  constexpr double epsilon = 1e-10;
   if (norm >= 1.0 - epsilon)
   {
     axis = axis / (norm + epsilon * norm);