World Space Position of a QEntity?

I have been playing with Qt3D, and I am struggling with how Transforms are handled. If two objects both have a QTransform applied, I can get the translation out of that, but the translation is done in terms of the parent's transform. So if I try to subtract the transforms of two objects with different parents, I won't get a vector between them. So how do I transform between parentspace and worldspace to be able to compute things like the transform of a red cylinder to represent a laser beam between two arbitrary objects?
It seems like I must be missing something pretty obvious.