From e96012523f1b7025213873ea8aef79f65bef8dbe Mon Sep 17 00:00:00 2001
From: Niels Dekker <N.Dekker@lumc.nl>
Date: Wed, 23 Mar 2022 17:21:09 +0100
Subject: [PATCH] STYLE: Encapsulate NiftiImage qto_xyz mat44 data as
 `Matrix<float,4,4>`

Using `itk::Matrix<float, 4, 4>` (instead of `std::vector<float>`) to
store the "qto_xyz" data from m_NiftiImage, as this `Matrix` template
instantiation more closely resembles the original niftilib `mat44` data
structure.
---
 Modules/Core/Common/include/itkMetaDataObject.h |  1 +
 Modules/Core/Common/src/itkMetaDataObject.cxx   |  1 +
 Modules/IO/NIFTI/src/itkNiftiImageIO.cxx        | 12 +++---------
 3 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/Modules/Core/Common/include/itkMetaDataObject.h b/Modules/Core/Common/include/itkMetaDataObject.h
index 8fab875c797..91023fc5e77 100644
--- a/Modules/Core/Common/include/itkMetaDataObject.h
+++ b/Modules/Core/Common/include/itkMetaDataObject.h
@@ -364,6 +364,7 @@ extern template class ITKCommon_EXPORT_EXPLICIT MetaDataObject<Array<char>>;
 extern template class ITKCommon_EXPORT_EXPLICIT MetaDataObject<Array<int>>;
 extern template class ITKCommon_EXPORT_EXPLICIT MetaDataObject<Array<float>>;
 extern template class ITKCommon_EXPORT_EXPLICIT MetaDataObject<Array<double>>;
+extern template class ITKCommon_EXPORT_EXPLICIT MetaDataObject<Matrix<float, 4, 4>>;
 extern template class ITKCommon_EXPORT_EXPLICIT MetaDataObject<Matrix<double>>;
 
 ITK_GCC_PRAGMA_DIAG_POP()
diff --git a/Modules/Core/Common/src/itkMetaDataObject.cxx b/Modules/Core/Common/src/itkMetaDataObject.cxx
index ab5b909f9e5..36c38a33cc7 100644
--- a/Modules/Core/Common/src/itkMetaDataObject.cxx
+++ b/Modules/Core/Common/src/itkMetaDataObject.cxx
@@ -43,6 +43,7 @@ template class ITKCommon_EXPORT MetaDataObject<Array<char>>;
 template class ITKCommon_EXPORT MetaDataObject<Array<int>>;
 template class ITKCommon_EXPORT MetaDataObject<Array<float>>;
 template class ITKCommon_EXPORT MetaDataObject<Array<double>>;
+template class ITKCommon_EXPORT MetaDataObject<Matrix<float, 4, 4>>;
 template class ITKCommon_EXPORT MetaDataObject<Matrix<double>>;
 template class ITKCommon_EXPORT MetaDataObject<std::vector<float>>;
 template class ITKCommon_EXPORT MetaDataObject<std::vector<double>>;
diff --git a/Modules/IO/NIFTI/src/itkNiftiImageIO.cxx b/Modules/IO/NIFTI/src/itkNiftiImageIO.cxx
index ac96e85de2f..c8d58a7e567 100644
--- a/Modules/IO/NIFTI/src/itkNiftiImageIO.cxx
+++ b/Modules/IO/NIFTI/src/itkNiftiImageIO.cxx
@@ -999,15 +999,9 @@ NiftiImageIO::SetImageIOMetadataFromNIfTI()
 
   EncapsulateMetaData<float>(thisDic, "qfac", nim->qfac);
 
-  std::vector<float> qto_xyz;
-  for (int row = 0; row < 4; ++row)
-  {
-    for (int column = 0; column < 4; ++column)
-    {
-      qto_xyz.push_back(nim->qto_xyz.m[row][column]);
-    }
-  }
-  EncapsulateMetaData<std::vector<float>>(thisDic, "qto_xyz", qto_xyz);
+  // Use the ITK Matrix template instantiation that matches the `mat44` typedef from niftilib.
+  using Matrix44Type = Matrix<float, 4, 4>;
+  EncapsulateMetaData<Matrix44Type>(thisDic, "qto_xyz", Matrix44Type(nim->qto_xyz.m));
 }
 
 void