Newbie Loft issue

 From:  Michael Gibson
2219.10 In reply to 2219.4 
Hi how - that sucks about getting laid off, but at the same time it is cool that you're focusing on learning new tools!

Like Danny mentions it can be a good idea speed-wise to use the "solid modeling" tools when possible, which basically means starting with a larger primitive solid shape made by something like extrusion, then using booleans and fillets/chamfers to modify the solid.

One common thing to use for stuff like that is to draw a curve and then do a boolean of the solid with the curve as the cutting object, to slice the solid up where the curve is projected on to it.

There is nothing wrong with doing a "surface modeling" approach where you do stuff like build individual surfaces and then join them, but it can take longer to finish, the solids tools are kind of like a "batch" operation. Like for instance doing a boolean with a circle curve as a cutting object does a kind of batch of extrusion + trimming + joining pieces together all in one sort of "higher level" operation.

One thing I've noticed is that people with a heavy poly modeling background do tend to focus on the "low level" surface construction tools more than thinking of using the solid modeling tools. It's certainly understandable since booleans and cutting operations tends to be generally avoided in poly modeling. In NURBS modeling they tend to be much more of a "first class citizen" and more of something to try first, that is one of the biggest differences in optimal workflow.

Another semi-related area is if you're trying to build a more complex model with some smoothly curved surfaces in them. In NURBS modeling you generally want to try to identify some larger kind of "panel sheets" that make up the overall form of your shape (as a kind of extended and simplified panel) and trim that to make many of the final edges in the model, rather than trying to do something like Loft or Sweep directly along irregular boundaries, which is more trying to build things directly to the final edges rather than producing those final edges through intersections. A sort of avoidance of intersections is another thing that I see often with people from a poly background.

Here are some examples of generating something through building extended panels and then intersecting them:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2164.2
http://moi3d.com/forum/index.php?webtag=MOI&msg=2164.4


One other area that tends to be a bit strange for poly modelers is the way that "underlying surfaces" work in NURBS. That means that you some edges of your surface may be a "Trim curve" that lives on the surface, and the surface can be larger and not necessarily have any of its surface control points actually aligned with that edge. That's why you can't typically just grab any edge vertex point of a NURBS model and just move it around like you would on a poly model, because that edge can be kind of floating somewhere interior to the surface rather than being one of the surface's own natural edges. But the payoff of this system is that this is fundamentally what makes Boolean operations work better in NURBS than on polygons, because when you do cuts of a surface it only calculates new trim curves and the underlying surface itself remains exactly the same. So the surface itself does not "degrade" with repeated trims or booleans like it does with polygons where you get fragmentation with each cut. Some more details and illustrations on the underlying surface structure here.


Anyway those are just some common issues for people coming from a poly modeling background, hope some of this is useful!


- Michael