No, just lines and using methods like Geom::intersect_line_plane and then checking weather the intersection lies withing the face itself. It's complicated and error prone (When lines intersect edges instead of faces) but can be made to work.

I've actually gone and changed my first post so that semi colons are allowed, and have modified your magic formula so the 3 steps are all in one line. I wanted no semicolons to avoid people going crazy with them (you could essentially write a whole program with them in one line of text). How about 3 semi colons maximum?

@Thomthom: Great thread! All this OOP and geometry, I can't help but feel it verges on mental masturbation . It's almost metaphysical. I'll be using a bit of code from that thread. Thanks @TIG: The short answer is I'm trying to find the transformation of a lot of things. I'll give you some background. I'm trying to create a kind of project space for CNC manufacturing. The hiearchy looks something like this. ->MODEL --->ASSEMLY (Group/Component) ----->WORKPIECE (Component) ------->DESIGN (Group) --------->TOOLPATH (Group/Component) ----------->HOLE (Group/Component) Some things are forbidden. A toolpath can't contain any other groups or instances, a workpiece can't contain another workpiece. But I want to allow the user to further nest whatever they want. This means a workpiece can have a group of toolpaths or an assembly can have workpieces that are nested in other groups. At the risk of rambling on, I'll leave it at that. Let me know if I'm not clear (which is often the case when I try to explain anything related to OOP )

Sorry for rehashing old problems. I did look around the forums. Guess I just wasn't looking properly. Your reply was clear and concise TIG. I tried your code out and it worked a charm. Cheers!

Thanks for the info and reference to vCarve. Been interested in CNC for a long time, and hope to be in a position to invest in a machine sometime over this next year. SU/vCarve looks like a good software solution.

Do with the information? The only thing I will do as a direct result of getting an answer is having the wikipedia page changed. After all, we want wikipedia to be as accurate as possible now, don't we? I should mention that I am developping a SU plugin that involves using the CGAL library (Minkowski sums, boolean operations, envelopes...) and though knowing weather SU uses CSG is not imperative for my project it certainly helps me have a better understanding of how SU works under the hood.