BUG: Fix generated partial volumes misaligned with input volume node

This commit fixes how the generated PV tiffs are loaded, to ensure that
the partial volume nodes preserve the original RAS/LPS orientation of
the input volume node.

Previously, the generated tiff files were always loaded in LPS-like
orientation (e.g., the IJK-to-RAS Direction Matrix would have -1 in the
first two diagonal entries). This would work correctly on most data we
have tested against, when the data is also originally in LPS
orientation. However, for data this is inherently in RAS directions
(e.g., the IJK-to-RAS Direction Matrix would have 1 in the first two
diagonal entries), or for cropped volume nodes (cropping is observed to
flip the volume from RAS to LPS directions or vice-versa), the loaded
PVs would appear misaligned.

AutoscoperM/AutoscoperM.py

@@ -768,9 +768,17 @@ def onLoadPV(self):
                 )
                 return
 
+            # get the IJK to RAS direction matrix from original input volume
+            parentVolume = self.ui.volumeSelector.currentNode()
+            parentIJKToRAS = vtk.vtkMatrix4x4()
+            parentVolume.GetIJKToRASDirectionMatrix(parentIJKToRAS)
+
             for i in range(len(vols)):
                 nodeName = os.path.splitext(os.path.basename(vols[i]))[0]
                 volumeNode = slicer.util.loadVolume(vols[i])
+                # ensure we maintain the original RAS/LPS directions from the parent volume
+                volumeNode.SetIJKToRASDirectionMatrix(parentIJKToRAS)
+
                 translationTransformFileName = os.path.join(mainOutputDir, transformSubDir, f"{nodeName}_t.tfm")
                 scaleTranformFileName = os.path.join(mainOutputDir, transformSubDir, f"{nodeName}_scale.tfm")
                 if not os.path.exists(translationTransformFileName):