Some suggestions for future MOI versions ;)

 From:  Michael Gibson
3539.2 In reply to 3539.1 
Hi vinced, those are some great suggestions!

But some of them do not really work with the way that NURBS objects are fundamentally constructed.

For example, the way you are talking about adding in points to an "edge", and then pulling the edge around to deform stuff. That is a polygon modeling concept, the way a NURBS solid works is much different from a polygon model.

In a NURBS solid, the edge you see can be what is called a "trim edge" - it's something that marks areas of a surface as being active or inactive (with inactive areas being holes).

But the the thing that actually has points that you would yank around is the surface that the trim edges are living on.

Only in some special cases like a box do the edges and the "underlying surfaces" actually coincide. Once you have done something like trimmed or booleaned one part with another, you end up with trim curves that are not really aligned in any way (in the sense of sharing control points I mean) to the surfaces that they are living on.

It's a much different system than a polygon modeling system - in a polygon system the edge you see is a direct part of the polygon surface and not some separate thing, so with polygons it works better to do things like yank an edge around or add points to an edge, those are the same things as manipulating the polygon surface. But that's not necessarily the case with NURBS.


I've got some illustrations in This FAQ answer, which may help to better describe some of this stuff like an "underlying surface" and a "trim curve".


But basically, if you want to work on things in a polygon modeling type of way, that's something that just does not fit very well with the way that MoI's object system is set up.

So you may ask "why is MoI's object system set up in this completely different way" - well these same things are the reason why other things like boolean operations work so much better with NURBS objects than they do in a polygon modeling system.

In a NURBS modeling system when you trim a surface or do a boolean, the "underlying surfaces" actually stay all the same and only new trim curves are created on the surfaces to create different cuts and holes in them. You can even erase those trim curves later to recover the original underlying surface. It helps things a lot when pieces are cut that the underlying surfaces themselves don't get more complex like they do in a polygon modeler where the booleans have to create a lot more little tiny surface fragments because there isn't the concept of a "trim curve" in a poly modeler.

- Michael

EDITED: 16 May 2010 by MICHAEL GIBSON