Hi Shawn,
> But as for MOI, if my boss came to me and said, "This
> looks good, but move that edge over an inch." What
> would I do? Would I have to start over?
Well, it depends on the situation - if the piece you have to change is pretty simple you can just build it over.
But you can also re-use existing surfaces as well - you can take some set of surfaces and break them off of the main object by using Edit > Separate, then move them over, remove the trim curves from the old areas, and then trim a new hole in the new spot and then join the pieces back together again.
There's an object repair tutorial here that covers that kind of low level surface trimming/untrimming and joining workflow here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=446.17
But if you think that's going to be a common thing to make modifications you may want to use one of the more regular solid modeling systems like SolidWorks / SolidEdge / etc... instead of MoI because those programs have systems in place for maintaining the history of how the object was constructed so you can go back and make modifications and have the model update.
In the future I do want to try to have some deeper history functions in MoI as well, but the overall focus in MoI right now is more on making it quick and easy to draw things initially. One of the negative side effects of those other solid modeling systems is that they're just more complex and tend to have somewhat more steps that you have to go through to create things. But if you need to make changes later on they work really well for that.
> I read in the FAQ how moving a point would tear faces
> away. What I don't understand is why the program can't
> just re-evaluate the surface based on the new location of
> the edge.
The problem is that unlike a polygon model, the edges do not define the surface at all - there is already a separate surface underneath the edges.
Here's an example - here I have a trimmed plane surface:
If I turn on control points for the surface, you can see that the underlying surface is a simple plane with just 4 corner points like this:
If you could edit edges directly, say you wanted to go in and pull this vertex upwards in z:
How then would the plane surface adapt to go through those deformed edges? There isn't any way to just move the surface's 4 control points to make the surface go through that modified edge. That's why you can't edit just any edge - if it's a trim curve it's just marking different areas of the surface as holes or solid areas, it's not defining the shape of the surface.
This is one of the things that's very different between polygon modeling and NURBS modeling - in polygon modeling the actual surface shape is completely defined by the edges, so moving the edges implicitly moves the surface as well, they are one and the same. In a NURBS model after you have done some booleans, you have trim curves which are a separate thing from the surface, there is a separate underlying surface that makes the surface shape and the trim curves are just markers on it.
But this system of an "underlying surface" and "trim curves" is basically what makes boolean operations work so much better with NURBS than with polygons because when you do a boolean with NURBS the underlying surface actually stays exactly the same as before, just new trim curves are calculated on it. Booleans with a poly modeler on the other hand actually dice the polygon surface up into smaller and smaller surface fragments with each boolean.
- Michael
