# Custom border extrapolation of ShapedImageNeighborhoodRange by ImageNeighborhoodPixelAccessPolicy

**URL:** <https://discourse.itk.org/t/custom-border-extrapolation-of-shapedimageneighborhoodrange-by-imageneighborhoodpixelaccesspolicy/879>\
**Category:** Engineering\
**Created:** [April 30, 2018, 6:02pm UTC](https://discourse.itk.org/t/custom-border-extrapolation-of-shapedimageneighborhoodrange-by-imageneighborhoodpixelaccesspolicy/879 "2018-04-30T18:02:39Z")\
**Posts on this page:** 1\
**Showing post:** 25

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**Author:** ![phcerdan](https://discourse.itk.org/user_avatar/discourse.itk.org/phcerdan/32/286_2.png) [@phcerdan](https://discourse.itk.org/u/phcerdan)\
**Post date:** [October 10, 2018, 9:41pm UTC](https://discourse.itk.org/t/custom-border-extrapolation-of-shapedimageneighborhoodrange-by-imageneighborhoodpixelaccesspolicy/879/25 "2018-10-10T21:41:44Z")

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Thanks Niels, crystal clear, I think I understood correctly the first time, but always appreciate the extra examples! 😊

So, better than talking, going directly for the code (simplified):

```cpp
template <typename TImage>
class ConstantBoundaryImageNeighborhoodPixelAccessPolicy final
{
//......... Appending to all the good stuff already there ...... //
public:
  void SetConstant(const PixelType & inputValue) {m_Constant = inputValue; }
}

```

No new template parameter in Range:

```cpp
template<typename TImage, typename TImageNeighborhoodPixelAccessPolicy >
class ShapedImageNeighborhoodRange final:
{
// ........ Appending .... //
TImageNeighborhoodPixelAccessPolicy & GetReferencePixelAccessPolicy() { return m_PixelAccessPolicy;}
}

```

The usage:

```cpp
// The equivalent in ITK 5.0 + this patch + this
// Using itk::Experimental::ShapedImageNeighborhoodRange:
using RangeType = ShapedImageNeighborhoodRange< ImageType,
ConstantBoundaryImageNeighborhoodPixelAccessPolicy<ImageType> >;

RangeType range{ *image, location, offsets}; // same constructor as before
range->GetReferencePixelAccessPolicy()->SetConstant(paddingValue); // we set the value at run time on the policy

```

Let me know what you think,  
Cheers

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