I noticed that the implementation of the method

void vtkMRMLVolumeNode::GetIJKToRASDirections(double dirs[3][3]);

declared in vtkMRMLVolumeNode.h:97 is missing in vtkMRMLVolumeNode.cxx

It would be something like

void vtkMRMLVolumeNode::GetIJKToRASDirections(double dirs[3][3])
{
for (int i=0; i<3; i++)
{
for (int j=0; j<3; j++)
{
dirs[i][j] = IJKToRASDirections[i][j];
}
}
}