Hi NightCabbage,

> Is there any reason why I can't just delete that blue
> circle, and have the yellow surface without that circular
> hole?

Actually you can do that - if that blue circle is a circular disk type surface, select it and delete it first, which will leave an empty hole. Then you can select the remaining edge in the yellow surface to "untrim" it and recover the underlying surface in that spot.

Here is one post that describes untrimming in more detail:
http://moi3d.com/forum/index.php?webtag=MOI&msg=444.4

Also here is a more complex mini tutorial that talks about using untrimming and re-trimming to repair an object that had a boolean done to it in an incorrect location:
http://www.moi3d.com/forum/index.php?webtag=MOI&msg=446.17


> Once again, the above is one solid object.
>
> But what if I wanted to change the shape of the exhaust?

You normally would just delete those faces that make up the exhaust and then construct a new one there instead.


> Or perhaps I want to move the whole exhaust to a different
> place on that flat surface?

You can basically detach the exhaust surfaces from the rest of the object by selecting those faces that make it up, and then using Edit/Separate. That makes those faces into an independent object which you can move somewhere else.

There's an object repair tutorial that goes into much more detail about this which is available here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=446.17


> Begin able to edit existing shapes by their internal
> components (lines and surfaces - though of course the
> surfaces are created automatically by the lines, but the
> surfaces should control the surrounding lines)

In the future I would like to make it possible to edit the model by moving edges around, but the way NURBS are structured it is not really an easy task to make that happen. It involves things like merging trimming boundaries, extending surfaces, stuff like that. That's because with a NURBS solid the edges that you see are not necessarily the edges of the "underlying surfaces", they may be trim curves which are just on the surface but not necessarily aligned with the surface's natural edge, which is a much different structure than how polygon meshes work.

There are some other NURBS modeling systems out there that have refined that kind of editing to a greater degree, one example is SpaceClaim, if that kind of editing is a big concern for you, you might want to check it out.

- Michael