ENH: make DerivativeThreshold variable

Author: romangrothausmann

include/itkSingleImageCostFunction.h

@@ -110,6 +110,10 @@ class ITK_EXPORT SingleImageCostFunction :
   itkSetConstObjectMacro( Image, ImageType );
   itkGetConstObjectMacro( Image, ImageType );
 
+  /** Get/set the DerivativeThreshold.  */
+  itkSetMacro( DerivativeThreshold, DerivativeType::ValueType );
+  itkGetConstReferenceMacro( DerivativeThreshold, DerivativeType::ValueType );
+
   /** Initialize the cost function */
   virtual void Initialize(void) throw ( ExceptionObject );
 
@@ -150,6 +154,7 @@ class ITK_EXPORT SingleImageCostFunction :
   /** Used to define the value outside the image buffer. Important when
    *  path points are on the edge of an image */
   ImagePixelType                              m_OutsideValue;
+  typename DerivativeType::ValueType          m_DerivativeThreshold;
 
 };
 

include/itkSingleImageCostFunction.hxx

@@ -33,6 +33,7 @@ SingleImageCostFunction<TImage>
   m_Image                 = nullptr;  // Provided by user
   m_Interpolator          = nullptr;  // Configured in Initialize()
   m_GradientImageFunction = nullptr;  // Configured in Initialize()
+  m_DerivativeThreshold   = 15.0;     // as in original implementation
 }
 
 
@@ -137,7 +138,6 @@ SingleImageCostFunction<TImage>
     }
 
   // Convert the image function output to the cost function derivative
-  constexpr typename DerivativeType::ValueType DerivativeThreshold  = 15.0;
   for (unsigned int i=0; i<ImageDimension; i++)
     {
     derivative[i] = static_cast<typename DerivativeType::ValueType>( output[i] );
@@ -146,7 +146,7 @@ SingleImageCostFunction<TImage>
     //           (indicated by very large values) which may skew the gradient.
     //           To avoid this skewing effect, we reset gradient values larger
     //           than a given threshold.
-    if ( itk::Math::abs (derivative[i]) > DerivativeThreshold )
+    if ( itk::Math::abs (derivative[i]) > m_DerivativeThreshold )
       {
       derivative[i] = 0.0;
       }