STYLE: Removed HoughTransform2DCircles default for TRadiusPixelType

ITK 4.13 introduced TRadiusPixelType as an extra template parameter
of HoughTransform2DCirclesImageFilter. It had a default argument,
TRadiusPixelType = TOutputPixelType, for ITK4 backward compatibility.
Unfortunately, this default argument is often not the right choice.
For OutputPixelType, an unsigned integer is often preferable, whereas
for RadiusPixelType, a floating point type is often a better choice.

This commit removes the default argument from TRadiusPixelType,
hoping to trigger ITK users to make the most appropriate choice.

Change-Id: I34d8b543815192700ad01c04d9c37df256ae2639

Examples/Segmentation/HoughTransform2DCirclesImageFilter.cxx

@@ -70,7 +70,8 @@ int main( int argc, char *argv[] )
 
   // Software Guide : BeginCodeSnippet
   using PixelType = unsigned char;
-  using AccumulatorPixelType = float;
+  using AccumulatorPixelType = unsigned;
+  using RadiusPixelType = float;
   constexpr unsigned int Dimension = 2;
   using ImageType = itk::Image< PixelType, Dimension >;
   ImageType::IndexType localIndex;
@@ -113,7 +114,8 @@ int main( int argc, char *argv[] )
 
   using HoughTransformFilterType =
     itk::HoughTransform2DCirclesImageFilter<PixelType,
-                                            AccumulatorPixelType>;
+                                            AccumulatorPixelType,
+                                            RadiusPixelType>;
   HoughTransformFilterType::Pointer houghFilter
                                             = HoughTransformFilterType::New();
   // Software Guide : EndCodeSnippet

Modules/Filtering/ImageFeature/include/itkHoughTransform2DCirclesImageFilter.h

@@ -52,15 +52,12 @@ namespace itk
  * is recommended, as the estimation of the radius involves floating point
  * calculations. Usually, 'double' is the best choice for this pixel type.
  *
- * By default, TRadiusPixelType = TOutputPixelType, in order to preserve backward
- * compatibility with ITK <= 4.12.2.
- *
  * \ingroup ImageFeatureExtraction
  *
  * \ingroup ITKImageFeature
  */
 
-template< typename TInputPixelType, typename TOutputPixelType, typename TRadiusPixelType = TOutputPixelType  >
+template< typename TInputPixelType, typename TOutputPixelType, typename TRadiusPixelType >
 class ITK_TEMPLATE_EXPORT HoughTransform2DCirclesImageFilter:
   public ImageToImageFilter< Image< TInputPixelType, 2 >, Image< TOutputPixelType, 2 > >
 {

Modules/Filtering/ImageFeature/test/itkHoughTransform2DCirclesImageTest.cxx

@@ -61,7 +61,7 @@ namespace
     constexpr double radius = 7.0;
     CreateCircle<ImageType>(image, center, radius);
 
-    using FilterType = itk::HoughTransform2DCirclesImageFilter< PixelType, PixelType >;
+    using FilterType = itk::HoughTransform2DCirclesImageFilter< PixelType, PixelType, PixelType>;
 
     const FilterType::Pointer filter = FilterType::New();
 
@@ -84,7 +84,7 @@ namespace
 
     using ImageType = itk::Image<PixelType>;
 
-    using FilterType = itk::HoughTransform2DCirclesImageFilter< PixelType, PixelType >;
+    using FilterType = itk::HoughTransform2DCirclesImageFilter< PixelType, PixelType, PixelType >;
 
     const FilterType::Pointer filter = FilterType::New();
 
@@ -136,9 +136,8 @@ namespace
 
     using OutputPixelType = unsigned long;
 
-    // By default, the radius image has the same type as the output image (the accumulator image).
     // FilterType2 has 'double' as radius pixel type, allowing a slightly more accurate radius estimation.
-    using FilterType1 = itk::HoughTransform2DCirclesImageFilter< InputPixelType, OutputPixelType >;
+    using FilterType1 = itk::HoughTransform2DCirclesImageFilter< InputPixelType, OutputPixelType, unsigned long >;
     using FilterType2 = itk::HoughTransform2DCirclesImageFilter< InputPixelType, OutputPixelType, double >;
 
     const FilterType1::Pointer filter1 = FilterType1::New();
@@ -356,7 +355,7 @@ int itkHoughTransform2DCirclesImageTest( int, char* [] )
 
   // Define the HoughTransform filter
   using HoughTransformFilterType = itk::HoughTransform2DCirclesImageFilter< HoughSpacePixelType,
-    HoughSpacePixelType >;
+    HoughSpacePixelType, HoughSpacePixelType >;
 
   HoughTransformFilterType::Pointer houghFilter = HoughTransformFilterType::New();