Well I don't understand much of it - but I don't think that it is what I had in mind. In OpenGL there should be either a menu like the other menus, or perhaps buttons "cut plane X-Y" and "cut plane Y-Z" or whatever - or as intelligent as in Tekla, where you just push "p" on your keyboard and then you choose a cuttingplane. And to move the plane you grab the scissor. An easy way to turn the sections on and off would also be nice. Try it out your self here: Tekla-model.http:// file://Groupinclu/intranet_pictures/Ramboll_Denmark_content/Site_menu/Projektsupport/Fagteknisk%20IT/3D/interaktiv_view/HOM/hom.html#
And see the attached pictures.