All notes
Itk

	displacementField->CopyInformation( fixedImage );
	displacementField->SetRegions( fixedImage->GetBufferedRegion() );
	displacementField->Allocate();
	displacementField->FillBuffer( zeroVector );

Note that SetRegions() is used to set all those regions altogether: bufferedRegion, LargestPossibleRegion.