Hi,
The rotation of scanned object with a mouse by holding down a mouse button and moving the mouse can be more intuitive by using the same mapping that is standard in most 3D CAD softwares (Such as SolidWorks, Creo, ProEngineer, OnShape) where the rotation is done in relation to the screeen coordinate system. When you hold down the mouse and move to the left, the object always rotates to the left, no matter what angle the object actually has or where you push down the mouse. Moving up and down is always also rotating the object up or down, in relation to the screen. To accomplish this, the software would have to map the screen coordinates to the object in correlation to the current direction of the object, and change this mapping as you move the mouse. Please try rotation in one of the mentioned CAD softwares and you will notice that it is easier to use. And it is much easier to get the object back to the direction that you started with.
By the way, using a space mouse (such as 3DConnexion that was mentioned in another thread) maps rotation the same way in the CAD softwares, when you spin it to the left, the object spins to the left in relation to the screen. This is also very intuitive to use.
Just a thought 