Hi Bill, re: selecting edge loops - what were you trying to do to the model when you were selecting edge loops? Are you trying to do adjust the shape or apply sub-d smoothing to this model instead of just rendering it?

The reason I ask is that you may not be able to use MoI's output for some kinds of editing tasks like that. If you want to do some editing involving sub-d smoothing where the edge topology is important to you, that may mean you need to create that topology directly inside of Modo rather than modeling in NURBS and then converting it into polygons. The NURBS to poly conversion result should be fine for just directly rendering the geometry though.


> Is the one rail sweep the best method for modeling
> an object like this?

Probably yes for getting it exactly as you have there.

You can use Rail revolve for making things very similar to this more quickly though - see the attached 3DM file.

First select this profile curve here (note you can arrange a sweep profile curve in the middle of a rail like this as well, that can be more convenient that putting it all the way at the end):



Then run Construct > Revolve > Rail Revolve, and pick the outer path as the rail curve:



Then for the revolve axis pick here:



That makes this:



But note that it's not quite 100% the same as your original, it's more symmetrical yours was kind of flared from the bottom to the top on the smaller tip areas.

- Michael

Hi,

I make quite a lot of models where the mesh is expected to be all quads. Some would say to use a poly program, and in some cases it can be easier, but that being said, there are models that are quite difficult to make in a poly program but a lot easier to make with MOI. So, I work around where I can. What I do is to cut up the model to force the mesher to create quads. Your model is quite easy and took about 10 mins for this example.

Pic showing mesh output.


The best thing is, not only do I get all quads, but also get the vertex normal info from the nurbs surface.

Hi Michael,
Yep, I was trying the sub-d smoothing.
I'm feeling out different options to see what works and what doesn't (that doesn't).
Thanks for clearing this up for me. It comes natural for me to overlook the obvious.
Thanks for your guidance and excellent software!
Bill

Cool Steve!
That is an excellent work flow you have there. It looks like a good way to go to get the best of both worlds!
Thanks,
Bill

Hi Steve, that's an interesting technique! Although it could be quite difficult to plan all the slices if the objects get much more complex. It seems that if something takes too much slice planning that could end up being the equivalent amount of work as creating the topology in the poly modeler...


Maybe another kind of similar approach could be to use polyline paths and profiles for the initial creation, that could make objects that are already diced up into several small surfaces. I've attached a sample model.

This has curves that look like this but they are actually just polylines instead of smooth curves:



Then when doing a sweep, it generates a result like this:



Then you might use some of the edge splitting tools in your poly modeler for splitting up the top big n-gon pieces.

- Michael

Hi Michael,

Yes, it does take some planning for more complex shapes, some I do make completely in a poly modeller. Just a case of which is the easiest/best result. Just as long as you realise that I do not cut up the model into all the actual quads, as there is no need for that. As example, this is just showing part of the model posted by Bill, I made 7 vertical cuts then let the mesher divide up the horizontal by angle in the output mesh settings.







Making the model with polyline paths can work, although you do then lose the vertex normal info(that you would get from the curved surfaces), and a need to then resort to smoothing groups.

- Steve

Hi Steve - aren't you going to lose the vertex normals anyway if you end up using the mesh as a control cage and apply sub-d smoothing?

Or are you generating quads for some purpose other than for use as a sub-d control cage?

- Michael

Hi Michael and Steve,
Wow! some good information here.

Michael, It doesn't appear that the sub-d smoothing messes up the normals.
Here is an image of a MoI object exported to .lwo and loaded into modo.
In modo I made a copy of the object, added a couple loop slices (to maintain
the sharp edges), then applied sub-d smoothing.




Thanks for the wonderful information.
Bill

Hi Steve,
Did you use trim to make the cuts?
From your earlier post I assumed you did that in modo, but it looks like the cuts were
actually made in MoI before exporting.
Thanks,
Bill

Hi Bill,

Yes, I used "Trim" in MOI on the various surfaces(edit: then joined them back together), then exported the mesh.

- Steve

Thanks Steve,
I like your work flow a lot. It is very helpful.
Bill

Hi Bill,

> Michael, It doesn't appear that the sub-d smoothing
> messes up the normals.

Yeah, I don't expect that they would get messed up, just that the original ones probably get discarded and brand new ones created that correspond to the sub-d surface.

In your case there the original hull and sub-d smoothed result are quite close to the same shape so it's hard to tell any difference in normals just by eyeballing it.

- Michael

Hi Michael,
-----------
>>Maybe another kind of similar approach could be to use polyline paths and profiles for the initial creation, that could make objects that are already diced up into several small surfaces. I've attached a sample model.<<
----------


In my original reply, I stated that "can work". I need to expand on that just in case Bill wants to try that method in the future.

First of all, when you created that sweep, you used a single cross section perpendicular to a one sweep rail, which then produces what you posted, however, problems arise when the ends of the surface(s) are not both on the same plane or not perpendicular for the sweep(as in Bills model). I will try to show some simple examples of the problems.

I have copied 2 curved edges from Bills model, then changed them to polylines(divided up by 16), then for simplicity, have added 2 lines at the ends for the cross sections.



Using one of the cross sections on a one rail sweep produces un-even(at top) spaced sections with a over-run at the other end.




If using the 2 cross sections on one rail, then at first glance it looks OK, but if you then check the top edge(zooming into box area)



There are broken edges. I placed a line(in yellow) snapping to the ends of the broken edges just to show it is not a display problem




If one or both of the cross sections are used on both rails, then there can be a problem, as where edges are expected, there may not be as they are smoothed.



- Steve

Hi Steve, yeah probably what you are running into there is if you have a high number of lines like that you probably have many of them that are within tolerance of being considered tangent to one another.

Segments that are considered tangent to each other will get kind of glommed together into longer rail pieces. It would probably be better for that rail segment combining stuff to not happen when the segments are lines.

If you had somewhat fewer lines so that they were not within such a close angle of being tangent to one another you might get a more expected result.

If you could post the 3DM model files of your examples I could test them over here and see if tuning up the rail segment combining solves the problem you are showing or not.

- Michael

Hi Michael,

I just used curves from the model Bill posted, have attached.
(Bills model still in there)

- Steve

Hi Steve, also probably 2-rail sweep is just not going to work for this purpose with segmented polyline rails - 2-rail sweep doesn't know how to produce mitered corners, when there is segmentation it's just going to build the equivalent of small sweeps individual sweeps along each pair of rails, I believe that's one of the problems that you were showing.

If you stick with some other tools like 1-rail sweep, lofting (between same # of segments), extrude, revolve, those would probably work better. Actually Network can work as well with the same number of segments on each side, that may give you what you a similar result that you would be thinking of from 2-rail sweep.

The way that 2-rail sweep works, it kind of drags a frame that slides along each of the rails as it moves along them - this surfacing mechanism just does not particularly have a good way to handle sharp creases in the rails other than in special cases like with rails that have the same shape.

- Michael

Hi Steve,

> I just used curves from the model Bill posted, have attached.

You can get a proper result from these curves by using Loft between these 2 pieces, instead of using 2-rail sweep:



That produces this result:




2-rail sweep just won't work in general for this particular purpose - here's an example with a smaller number of segments to show more clearly what will happen:





- Michael

Hi Michael,

The one rail sweeping does not work for this example, there are various problems.

Network gives the same result as 2 rail sweep in this example.


Not to worry, I am OK the way I do this already. I just wanted to point out possible problems to Bill.


- Steve

Hi Michael,

>>You can get a proper result from these curves by using Loft between these 2 pieces, instead of using 2-rail sweep:<<

Yes I know, but those (single)end lines where put in place to simplify the example of the sweep. Try using the actual curves from the edges of the model.

What about the broken edges from the one rail sweep using both end lines?(as shown in the pics)

- Steve

Hi Steve,

> The one rail sweeping does not work for this example, there
> are various problems.

For 1 rail sweep you'll probably want to do it with just 1 profile and a planar rail which will enable mitered corners. That means that you would make something like flared ends by slicing tips off of a more regular initial shape, rather that incorporating the angled end parts directly into the surface construction.


> Network gives the same result as 2 rail sweep in this example.

This is the one that I can probably tune up in v3, it's related to that combining together of things that are within a close angular tolerance of being G1. I think I should be able to detect the case that the inputs are made up only of line segments and make sure that the output has the same segmentation in it.

This is the one that if you had a bit fewer segments in the curves where each line was not so close to being tangent to its neighbor, you would not get that combining effect.

- Michael