Hi folks,

I have a huge problem with the network of a surface.

I think that the curves are not correctly intersecting, since I can only get one section of the intersecting curves to "surface".

I am pretty sure that I don´t have enough curves defining the surface, and that the curves are intersecting with themselves makes it hard for MOI to calculate the surface. I would of course "simplify" the set up, but when I open up the curves in the middle, the edges of the left and right side surface don´t intersect smoothly and I get a "valley" in the mesh.

In addition to this, I´d like to know if there´s a function to weld curves together into a mesh? I haven´t worked with a full fledged nurbs modeller before, I love it, but still have to figure out a lot.

Any help in this matter would be highly appreciated!

Thanks in advanve, even for just having a look at my problem!

Michael

Hi Michael, the way Network works requires a fully regular grid layout, which means that all the curves can be flattened down into a 2D grid pattern.

It's kind of similar to how curved latitude and longitude lines on a globe can be mapped to a flat 2D map with horizontal and vertical lines for each of them.

If you have something like this curve in yellow here:



Then you can't have something that only crosses it by some partial amount like this other one here:




What will happen in your case above is that some of the pieces will be considered be excess portions hanging off the end of the regular network and will get trimmed off.

To make a network you need to have a more regular grid pattern to the curves, more like this:




The curves should be clearly separated into 2 different groups (like latitude and longitude), and each member of one group should cross over all the curves in the other direction.

> In addition to this, I´d like to know if there´s a
> function to weld curves together into a mesh?

You mean so that you could pull around intersection points? No, that's really trying to process things more like a polygon mesh modeler would work.

Really the strongest area of NURBS modeling is when you are generating shapes and cutting things from 2D profile curves rather than a big bunch of curves swooping all around in 3D.

Also if you do have some 3D curves, you generally want to make more broad and simple surfaces from them and use booleans and trimming to put in some kinds of cutout details, rather than trying to build surfaces directly around hole outlines.

Frequently I see people with a polygon modeling background try to build things in a more "patch by patch" method with building surfaces that hug around a hole, rather than the NURBS way which is to make a big broad piece and then cut it.

Do you have an image or drawing of the model you are trying to create? That may help me to give you some more specific tips, but if your model has a lot of freeform nature to it and is not easily described by 2D profile curves, that could very well put it in a category of things that are more suited for sub-d/poly modeling with its focus of tweaking 3D mesh points around, rather than the profile curve driven strategies that are the best fit for NURBS.

- Michael

Hi Michael,

thanks for the reply!

Yes, I am one of those vertex and poly push n pullers ;)

And I already guessed what you told me, but tried anyway :D

So, the "correct" (if there is any) way would have been to first start with a basic shape and then "chisel" away and add material.

I attached my result so far, but my test version ran out before I was able to finish the project. No big deal since I did a poly version in another app, but still would have liked to have brought the project across the finish line.

If you have a look at it, let me know what you think ;)

Thanks,
Michael

Cool model!
(Colors are mine :)

Seems curious : position of the model to the general gride!

Mirror gives open intersections (I don't know if you want that)

Yeah, I know, I was kind of looking for an instance object to mirror the parts and then work on the model, but when I did not find one I just started modeling away without caring for the model not being aligned to the center axis of the modeling area.

I had a huge problem with connecting, joining, welding the surfaces, and if I´d start again I would really start with a primitive and then building up the model from there.

As written before I was not able to finish the model, since my 30 days were up :( Maybe I´ll continue when the next demo version is available for 3.0 or so ;)

Hi Michael,

> So, the "correct" (if there is any) way would have been to
> first start with a basic shape and then "chisel" away and
> add material.

Yeah, but that method of "build a larger basic shape then cut it" is particularly what you want when your surfaces have a more irregular boundary, like if some pieces are shaped pretty differently than others, or there are things like notches or holes cut out.

But if your model does decompose well into strips, then building it strip by strip is fine.

With NURBS you just don't want to try and build surfaces around what looks like a hole - instead you build a full sheet pretending that the hole isn't there, and then cut out the hole with a trim or boolean operation. That's one of the major differences with NURBS modeling versus polygon modeling since in polygon modeling you usually try to avoid booleans, while in NURBS modeling they are usually more of a primary strategy.

It look like you were making some good progress on your model!

- Michael

Michael,

thanks for the comments! Just as usual, old habits never die (easy) So I started wayyy to complicated by modeling like I usually do.

And yes, almost there, but then time ran out :cry Ah well, maybe I´ll revisit it and finish it one day.

What kind of really bugged me was that I could not figure out how to weld the various surfaces at the edges, leading to a bad polygon flow and of course an open mesh on export. Any tips on how to do that properly?

Thanks,
Michael

Hi Michael,

> What kind of really bugged me was that I could not figure out
> how to weld the various surfaces at the edges, leading to a bad
> polygon flow and of course an open mesh on export. Any tips
> on how to do that properly?

You would normally use the Edit > Join command to do that - that can take surfaces that are touching each along an edge to get joined into a larger structure that has a single common edge between the 2 surfaces.

Then when meshing those joined edges will be treated specially so that they get a common vertex structure in those areas making a "watertight" mesh.

But you've got to have surface edges that match up to within 0.005 units of one another in order for them to be joinable.

In some areas you've got surfaces kind of sticking past one another like here:



That piece sticking out there would need to be trimmed off first before those could be joined.

Also if you're using Network in this kind of "patch by patch" construction process you can additionally run into a problem where Network uses a somewhat looser tolerance than some other commands in order to make a surface result that is not overly dense with control points. But it can sometimes just barely sag away by more than the 0.005 join tolerance. In those cases with this particular Network problem, you can work around the problem by scaling the objects you want to join by 1/10 in size (which also scales down the gap between surfaces), then do the Join, and the scale back up.

This is all quite a bit easier if you work more with solids from the start rather than doing things at this kind of individual surface modeling level which is kind of a more advanced (and also finicky) approach.

If you keep things as solids and carve pieces off of the solids with boolean functions, then you don't need to join things together because everything stays as an already joined solid at every step.

So for example if you watched the video tutorials here:
http://moi3d.com/2.0/docs/tutorials.htm , notice that they work by creating some different solid pieces and then combining them with booleans - then there is no joining step in that kind of workflow.

Your particular project being a helmet made of something like hammered and contoured sheet metal is getting kind of somewhat more in the "organic modeling" territory than something that would be machined which is where the NURBS solids tools become much more of a strength.

- Michael

Hi Michael, so in your case it looks like you would need to use the scale down + join + scale back up case to get it to join well.

There are a couple of things like that extending spot I showed earlier that are not ready to join, but other than that these parts here can be joined:



There is a little slivery hole right here though where there seems to be a missing surface:




But anyway, I've attached the results after joining, and also an OBJ file that was created from the joined result, you should be able to see now that there aren't any cracks in the mesh anymore (aside from that sliver above).

- Michael

Hi Michael,

thanks a lot !

I somehow must have messed up on my way. I actually tried always to snap the end points of my curves on the respective other curves to make the surfaces closed and defined. That was where I tried to aim for in my initial question, since once I have a complex network set up, and skinned the thing, but choose to move one curve or curve point, I very likely loose the "watertightness" of the model. I never figured out how to keep all surface curves aligned at once, so it was a constant hopping around and checking if there are holes anywhere.

I´ll just download the no-save trial version and see if i can reproduce your advice.

Thanks again for the OBJ-files, I´ll check them in Cinema4D!

Michael