Top 10 reasons for buying MoI...
 1-10  11-22

Previous
Next
 From:  Dave Morrill (DMORRILL)
2704.11 In reply to 2704.8 
> But generally Modo is pretty good in this area, its n-gon triangulation failures tend to be pretty rare, and small in number.

> If you can isolate it down to a small example, it would probably be good to send it to luxology so they could do something to fix it up.

Well, after reading Frenchy Pilou's suggestion, I decided to try a create a simple failure case to send you. The good news is that everything I tried worked fine (sort of). So it is not what I thought it was (simple non-convexity). The "sort-of" qualifier refers to the fact that I could consistently create cases where the ngons were there, but in some kind of a strange "flipped" state. I say "strange" because selecting the bad ngon and flipping it did not fix the problem. But if you flipped it a second time, then everything was OK. That's not such a horrible problem, because it only takes a couple of seconds to fix (once you know to "flip it" twice). However, I'll try and send the example to Luxology to look at.

So then I went back to the original, more complex, MoI file that I had observed having a real problem when loaded into modo. Well, the file had a problem when loaded back into MoI as well. There were some strange faces sticking out of the geometry in a couple of places. Zooming into the nook and crannies, I noticed that I had probably applied a slightly too large fillet around the edges of some text I had booleaned into an object, and in some of the corner creases it was causing some problems. Didn't really see it when I applied the fillet though. So I guess it was my bad after all.

> One other thing you might try when you run into this (which should hopefully be only an occasionally seen thing rather than the norm) is to use the "Divide larger than" parameter in MoI to dice polygons up and alter their structure. If you enter in a distance for "Divide larger than", any polygons larger than that size will be diced down, which tends to also cut complex n-gons into less complex n-gons.

Yes, this is a great feature that I have already had occasion to use. I had created a surface with a very subtle curve that ended up being a single ngon on export. Since I didn't want it to appear to be perfectly flat, I began experimenting with some of the "slice and dice" features in the dialog and quickly solved the problem. Like you said, you probably don't need to use them often, but it's really nice having them there when you do.

> Yeah, I would like to have this in the future... It's unfortunately not always so easy for me to get this information, often times the operation that failed is some low level thing way deep down in one of the geometry library's algorithms and it is not easy to try and record the specific problem all the way from the "top level view" from the code...

Oh, I see. I had forgotten that most of your code is sitting on top of a 3rd party library. Well, you can always give an error similar to one that one of the C compilers back in the 80's used to give me: "Syntax Error: Program expected." ;-)

Dave Morrill
  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged

Previous
Next
 From:  Dave Morrill (DMORRILL)
2704.12 In reply to 2704.10 
> I'd recommend using .lwo format instead - that will likely eliminate the problems you are currently seeing.

OK, I'll definitely give that a try. The .obj format seemed to work for 90% of the stuff I tried, so I never got around to trying .lwo.

Thanks for the tip!

Dave Morrill
  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged

Previous
Next
 From:  Michael Gibson
2704.13 In reply to 2704.11 
Hi Dave, just a note on this part:

> I say "strange" because selecting the bad ngon and flipping
> it did not fix the problem. But if you flipped it a second time,
> then everything was OK.

Yeah, getting that result is due to one of the bugs in Modo's OBJ importer.

In Modo's core functions, it is sensitive to which vertex of a polygon is set to the first one in the list of vertices.

Modo's core polygon normal calculator only looks at the edges radiating out from the very first vertex of the polygon in order to determine the polygon's normal. So with a complex n-gon, the first vertex must be set to a convex vertex in order to get the proper result.

As far as I can tell, Modo's OBJ importer fails to do that, which may result in an improperly oriented polygon in Modo.

When MoI exports to LWO format, it does this work to set the starting point of the n-gon to a good location for Modo/LightWave's orientation mechanism. So that's why this problem is avoided when using LWO export instead currently.


Since Modo has this sensitivity to which point is the first point, it would be a good idea for their OBJ importer to be aware of that and set the first point to match what their core engine expects...

But also another good improvement would be for them to tune up the core normal calculation so that it is not so sensitive to which point happens to be the first one in the list.

The reason why doing the flip twice works, is that there is a mechanism in Modo's flip function where if you do it the second time it will do some work to figure out a good start vertex for the ngon and rotate the points in the list so that one is first.

Some other discussion on this here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2039.5

- Michael
  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged

Previous
Next
 From:  PaQ
2704.14 In reply to 2704.12 
Hi Dave,

You should be lucky with the .obj in modo, because I've got thousands of n-gones problems when using this format.
As Michael said, .lwo is much better, I can't remember when I had a flipped poly using it ... but still it may happends.

So I'm still doing an geometry>poly>align when importing .lwo object ... it works as a double flip you descibe, but it's an 'autmaic' way
so it will resolve normal problem on area you don't always notice at first sight. (Can be frustrating to discover a wrong poly after an hires rendering of 4 hours for exemple).
  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged

Previous
Next
 From:  Michael Gibson
2704.15 In reply to 2704.14 
Hi PaQ,

> As Michael said, .lwo is much better, I can't remember when
> I had a flipped poly using it ... but still it may happends.

Right now I don't have any reports of improper flipped polygons when using LWO format...

So I'd think that extra geometry>poly>align step should not be needed if you are using LWO format, but by all means if it makes you feel better... ;)


There are a couple of issues that can come up which are not actually bugs though, like if you export an open surface rather than a closed solid, it may not have the normal orientation like you expect because only solids have an automatic "outside" direction applied to them.

Also if you have 2 independent surfaces in MoI that are sitting side by side and not actually joined to have a common edge, then the meshes are generated separately and may not have the same normal orientation between them. When objects have joined edges, the polygons will have a consistent direction between them though.


What I have seen on a couple of rare occasions is a triangulation failure where Modo did not handle splitting up a certain n-gon into display triangles properly. This is a different problem than a normal orientation one, but it is also very unusual to run into it.

- Michael
  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged

Previous
Next
 From:  Jason (JCLARK)
2704.16 In reply to 2704.15 
In general, exporting from MoI is going to be fine for stills. However, if you expect to animate and deform your meshes you will have to get a good topology tool. Bang for the buck going MoI + SILO, or MoI+3DCoat would allow you to get your NURBS models into a program that you can tailor the polygons by retopologizing.
- Jason
http://www.jasedesign.com http://www.nurbsandpolys.com http://www.cgpipeline.com
  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged

Previous
Next
 From:  PaQ
2704.17 In reply to 2704.16 
Hi Michael, ... well indeed maybe I have developed some OCD about poly normals :o)

I'm not quite sure what kind of mesh I will build in MOI if I know I have to do some deformation/animation with ... until ... I tried to export a model in ngone + divide larger than option ... the result is quite cool Oo


EDITED: 3 Feb 2010 by PAQ

  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged

Previous
Next
 From:  PaQ
2704.18 In reply to 2704.17 
the original model was less funny =O)

EDITED: 3 Dec 2015 by PAQ

  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged

Previous
Next
 From:  Michael Gibson
2704.19 In reply to 2704.16 
Hi Jason, yeah like PaQ shows you can use the "Divide larger than" function in MoI's exporter to ensure that large polygons are diced up into smaller evenly sized pieces.

That can make a result that should be suitable for non-rigid-body type animations without necessarily needing to retopologize.

Certainly if you have a very specific kind of animation where you want one individual piece to move in a certain way it could be a good idea to retopologize that area though...

- Michael
  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged

Previous
Next
 From:  Jason (JCLARK)
2704.20 In reply to 2704.19 
Good point, good to try first without doing topo again.

What I like though is that MoI is getting to be an artists tool, so keeping in mind that MoI can play nice with modo, 3DC, SILO is a good thing.
- Jason
http://www.jasedesign.com http://www.nurbsandpolys.com http://www.cgpipeline.com
  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged

Previous
Next
 From:  Dave Morrill (DMORRILL)
2704.21 In reply to 2704.13 
> Hi Dave, just a note on this part...

Thanks for the detailed explanation, Michael!

I'm definitely switching over to using .lwo format from now on...

Dave Morrill
  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged

Previous
 From:  Dave Morrill (DMORRILL)
2704.22 In reply to 2704.14 
> So I'm still doing an geometry>poly>align when importing .lwo object ... it works as a double flip you descibe, but it's an 'autmaic' way
so it will resolve normal problem on area you don't always notice at first sight. (Can be frustrating to discover a wrong poly after an hires rendering of 4 hours for exemple).

Thanks for that tip, PaQ! I think I had tried 'align' on a Bonzai 3D model when I was evaluating it (they tend to produce lots of flipped polys all over the mesh), but it didn't seem to have any effect on the flipped polys. It's good to know that it fixes the problems if and when they occur in a MoI import.

Is there any trick to using 'align'? I think when I tried it on the B3D mesh I did not have any geometry selected. That is, since nothing was selected, I assumed it would work on the entire mesh in this case. Is that the right way to use it, or should I have something selected before using it?

Dave Morrill
  Reply Reply More Options
Post Options
Reply as PM Reply as PM
Print Print
Mark as unread Mark as unread
Relationship Relationship
IP Logged
 

Reply to All Reply to All

 

 
 
Show messages:  1-10  11-22