[Insight-users] Bug in void SpatialObject< TDimension >::ComputeObjectToParentTransform()

[Bloch Christoph]

Hi all,

there is a bug in the current implementation of the method. The code
attached below indicates, that calling
ComputeObjectToParentTransform() after ComputeObjectToWorldTransform()
changes the ParentToWorldTransform which it should not - at least to my
understanding.

#include "itkSpatialObject.h"
#include "itkGroupSpatialObject.h"

using namespace std;

int main( int , char *[] )
{
  typedef itk::SpatialObject<2>             SpatialObjectType;
  typedef SpatialObjectType::TransformType  TransformType;

  SpatialObjectType::Pointer object1 = SpatialObjectType ::New();
  object1->GetProperty()->SetName("First Object");

  SpatialObjectType::Pointer object2 = SpatialObjectType ::New();
  object2->GetProperty()->SetName("Second Object");
  object1->AddSpatialObject(object2);

  SpatialObjectType::Pointer object3 = SpatialObjectType ::New();
  object3->GetProperty()->SetName("Third Object");
  object2->AddSpatialObject(object3);


 TransformType::OffsetType ObjectToWorldOffset;
 ObjectToWorldOffset[0] = 5;
 ObjectToWorldOffset[1] = 5;

 object1->GetObjectToWorldTransform()->SetOffset(ObjectToWorldOffset);
 object1->ComputeObjectToParentTransform();
 object1->ComputeObjectToWorldTransform(); //update all children

cout << object1->GetObjectToParentTransform()->GetOffset() << endl;
cout << object2->GetObjectToParentTransform()->GetOffset() << endl;
cout << object3->GetObjectToParentTransform()->GetOffset() << endl;


cout <<"\nCalling object3->ComputeObjectToParentTransform()\n" << endl;
object3->ComputeObjectToParentTransform();

cout << object1->GetObjectToParentTransform()->GetOffset() << endl;
cout << object2->GetObjectToParentTransform()->GetOffset() << endl;
cout << object3->GetObjectToParentTransform()->GetOffset() << endl;


return 0;

}

This gives the following output:

[5, 5]
[0, 0]
[0, 0]

Calling object3->ComputeObjectToParentTransform()

[5, 5]
[0, 0]
[5, 5]

I think I tracked the problem down to the following code:
void
SpatialObject< TDimension >
::ComputeObjectToParentTransform()
{

  m_ObjectToParentTransform->SetScale(m_ObjectToWorldTransform->GetScale());
  m_ObjectToParentTransform->SetCenter(m_ObjectToWorldTransform->GetCenter());
  m_ObjectToParentTransform->SetMatrix(m_ObjectToWorldTransform->GetMatrix());
  m_ObjectToParentTransform->SetOffset(m_ObjectToWorldTransform->GetOffset());

  if(m_TreeNode->HasParent())
    {
    typename TransformType::Pointer inverse = TransformType::New();
    if(static_cast<TreeNodeType*>(m_TreeNode->GetParent())
449:       ->GetNodeToParentNodeTransform()->GetInverse(inverse))
      {
551:      m_ObjectToParentTransform->Compose(inverse,true);
      }
    }
......

Here line 449 should be changed to
->GetNodeToWorldTransform()->GetInverse(inverse))
and line line 451 to
m_ObjectToParentTransform->Compose(inverse,false);

I hope this saves some headache,
Christoph