ENH: Let ImageSpatialObject update the image regions of its base class

`SpatialObject` stores the image regions of the spatial object. It appears
reasonable for its derived class `ImageSpatialObject` to keep them up-to-date,
in accordance with its image.

Modules/Core/SpatialObjects/include/itkImageSpatialObject.h

@@ -124,6 +124,10 @@ class ITK_TEMPLATE_EXPORT ImageSpatialObject : public SpatialObject<TDimension>
   SetInterpolator(InterpolatorType * interpolator);
   itkGetConstMacro(Interpolator, InterpolatorType *);
 
+  /** Updates the regions of this spatial object in accordance with its current image, and calls its Superclass. */
+  void
+  Update() override;
+
 protected:
   /** Compute the boundaries of the image spatial object. */
   void
@@ -149,6 +153,10 @@ class ITK_TEMPLATE_EXPORT ImageSpatialObject : public SpatialObject<TDimension>
 
   typename InterpolatorType::Pointer m_Interpolator{};
 
+  /** Updates the regions of this spatial object in accordance with its current image. */
+  void
+  UpdateImageRegions();
+
 #if !defined(ITK_LEGACY_REMOVE)
   template <typename T>
   void

Modules/Core/SpatialObjects/include/itkImageSpatialObject.hxx

@@ -149,6 +149,8 @@ ImageSpatialObject<TDimension, PixelType>::SetImage(const ImageType * image)
     }
 
     m_Image = image;
+    UpdateImageRegions();
+
     if (m_Interpolator)
     {
       m_Interpolator->SetInputImage(m_Image);
@@ -185,6 +187,32 @@ ImageSpatialObject<TDimension, PixelType>::InternalClone() const
   return loPtr;
 }
 
+
+template <unsigned int TDimension, typename PixelType>
+void
+ImageSpatialObject<TDimension, PixelType>::Update()
+{
+  UpdateImageRegions();
+
+  // Call the Superclass Update() after (not before) updating the image regions! The effect of Superclass::Update()
+  // may depend partially on the image regions.
+  Superclass::Update();
+}
+
+
+template <unsigned int TDimension, typename PixelType>
+void
+ImageSpatialObject<TDimension, PixelType>::UpdateImageRegions()
+{
+  if (m_Image)
+  {
+    Superclass::SetLargestPossibleRegion(m_Image->GetLargestPossibleRegion());
+    Superclass::SetBufferedRegion(m_Image->GetBufferedRegion());
+    Superclass::SetRequestedRegion(m_Image->GetRequestedRegion());
+  }
+}
+
+
 template <unsigned int TDimension, typename PixelType>
 void
 ImageSpatialObject<TDimension, PixelType>::PrintSelf(std::ostream & os, Indent indent) const

Modules/Core/SpatialObjects/test/itkImageMaskSpatialObjectGTest.cxx

@@ -351,3 +351,47 @@ TEST(ImageMaskSpatialObject, IsInsideInWorldSpaceOverloads)
               imageMaskSpatialObject->IsInsideInWorldSpace(point, 0, ""));
   }
 }
+
+
+// Check that regions of the mask image are stored in the spatial object.
+TEST(ImageMaskSpatialObject, StoresRegionsFromMaskImage)
+{
+  using ImageMaskSpatialObjectType = itk::ImageMaskSpatialObject<>;
+  using MaskImageType = ImageMaskSpatialObjectType::ImageType;
+
+  // Test image regions of various indices and sizes:
+  for (const itk::IndexValueType indexValue : { -1, 0, 1 })
+  {
+    // Just test some small sizes, to make the test run fast:
+    for (itk::SizeValueType sizeValue{ 2 }; sizeValue < 4; ++sizeValue)
+    {
+      using RegionType = MaskImageType::RegionType;
+      using IndexType = MaskImageType::IndexType;
+      using SizeType = MaskImageType::SizeType;
+
+      // Create a mask image.
+      const auto maskImage = MaskImageType::New();
+      maskImage->SetRegions(RegionType{ IndexType::Filled(indexValue), SizeType::Filled(sizeValue) });
+      maskImage->Allocate(true);
+
+      const auto imageMaskSpatialObject = ImageMaskSpatialObjectType::New();
+      imageMaskSpatialObject->SetImage(maskImage);
+
+      EXPECT_EQ(imageMaskSpatialObject->GetLargestPossibleRegion(), maskImage->GetLargestPossibleRegion());
+      EXPECT_EQ(imageMaskSpatialObject->GetBufferedRegion(), maskImage->GetBufferedRegion());
+      EXPECT_EQ(imageMaskSpatialObject->GetRequestedRegion(), maskImage->GetRequestedRegion());
+
+      // Modify one of the image regions.
+      maskImage->SetRequestedRegion(RegionType{ IndexType::Filled(indexValue + 1), SizeType::Filled(sizeValue - 1) });
+
+      // Note: when an image region is modified _after_ calling SetImage, the user must call Update() to keep the
+      // regions of the spatial object up-to-date.
+      imageMaskSpatialObject->Update();
+
+      // Do the same checks after the Update():
+      EXPECT_EQ(imageMaskSpatialObject->GetLargestPossibleRegion(), maskImage->GetLargestPossibleRegion());
+      EXPECT_EQ(imageMaskSpatialObject->GetBufferedRegion(), maskImage->GetBufferedRegion());
+      EXPECT_EQ(imageMaskSpatialObject->GetRequestedRegion(), maskImage->GetRequestedRegion());
+    }
+  }
+}