Copy and Paste works well now. Areas of voxels can be grouped to new entities for placing them in the scene. The size of the entire voxel data of the screenshot below on disk is just 1.3MB, which is quite OK. Thanks to my new graphics card, voxel raycasting and terrain rendering also runs smoothly at 60+ fps at full HD resolution now. Also worth a note: The raycasting method is updated to allow octrees greater than 16 levels - the scene below is created in an 18 level octree. Now, problems with precision begin to arise, which need to be solved.