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 From:  TpwUK
7616.1 
I have tried numerous ways to close this object to a solid but no matter what i do I will end up with between 8 and 29 naked edges. I have included the 3DM model that has just the eight bad edges.

Martin
(TpwUK)
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 From:  BurrMan
7616.2 In reply to 7616.1 
Here's one. There are definitely tangency issues, but the original has them.. But this is a solid.....
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 From:  TpwUK
7616.3 In reply to 7616.2 
Thank you BurrMan, I don't know how you fixed it to be solid, it still shows 2 naked edges here but it does indeed say solid.

I can now carry on with more booleans :)

Thanks again

Martin
(TpwUK)
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 From:  BurrMan
7616.4 In reply to 7616.3 
I'll take a look at it again in a bit. If you want, we can discuss what I did. Basically rebuilt some of the surfaces with bad trim boundaries.
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 From:  TpwUK
7616.5 In reply to 7616.4 
I did try rebuilding surfaces, ShrinkTrimmedSrf, Merge and even creating new curves to build from. I know where the problem area lies but I can't get the curvature right which is why it ends up as three surfaces converging to a point. I will have to see how it looks as a mesh and try and fix it there when the rest of the model is complete :/

Martin
(TpwUK)
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 From:  BurrMan
7616.6 In reply to 7616.5 
Hi Martin.... FYI the naked edges are registering because there is a little floating surface inside of the solid... If you do a window select over the top 1/3 of the solid, it will select that surface and you can delete it......
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 From:  TpwUK
7616.7 In reply to 7616.6 
Nice one! - Thank you again :)

Martin
(TpwUK)
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 From:  keith1961
7616.8 
Hi
What is a naked edge? I know you solved this issue but I took a look and found a faces that seemed to overlap (see picture) that I used to produce when I tried to stitch surfaces together to make a solid rather than making solids and chopping them up in various ways. I made a rough example of a lofted grip that I think with some extra points for the curved portions would be a possible approach to modeling the object.
Keith
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 From:  TpwUK
7616.9 In reply to 7616.8 
Hi Keith, a naked edge is where a surface meets another surface but fails for whatever reason to share a common boundary/edge to unite those surfaces ... Or at least I think that's what it means. Angular surfaces like the ones you posted don't tend to suffer naked edges as such, but tend to fail because end points don't meet or that they are not planar. Naked edges tend to be created by fillets and trimming and is more of a computational failure than poor operator/user geometry, although after saying that, poor workflow, such as my original post can and in some cases does increase the probability of leaving little slithers of surfaces or edges behind that confuses things resulting in one or more naked edges.

If i am wrong here, my apologies. Hopefully someone more knowledgeable than me can correct this too if i am :)

You can get a copy of the shortcut key command that shows naked edges from here http://kyticka.webzdarma.cz/3d/moi/


Martin
(TpwUK)
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 From:  keith1961
7616.10 In reply to 7616.9 
Thanks Martin
I'm using the script now.
Keith
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 From:  Michael Gibson
7616.11 In reply to 7616.9 
Hi Martin, re: naked edges - that's a good description but maybe a bit simpler way to describe it is a naked edge is when an edge belongs to just one single surface rather than being joined between 2 surfaces.

It's not automatically an error to have naked edges - if you just draw a simple rectangular plane using Draw solid > Plane, that will have 4 naked edges which is normal and expected because it's just a single surface and not joined to anything yet.

But if your object is supposed to be a watertight solid, that's when there are not supposed to be any naked edges and you can use that script to find areas where things are not joined properly, either because of an unexpectedly large gap between edges leaving a hole there, or sometimes due to some kind of bad trimming boundary like one that criss-crosses over itself or has an edge squeezed down to a single point or some various things similar to that.

So anyway if you have a goal to make your object a finished solid and it does not show as "Solid" in the object type indicator in the properties panel, that means it has some naked edges in it which you can use that script to locate. Those areas then usually need some repair work on them.

- Michael
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 From:  TpwUK
7616.12 In reply to 7616.11 
Thanks Michael - Much better put than my version :)

Martin
(TpwUK)
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 From:  keith1961
7616.13 In reply to 7616.12 
In my quest to find out more about meshes I found this:

"Distant Unicorn (History|Contact)
Oct 27, 10 6:25 pm
Draw me an extruded pentagon in NURBS (perfectly quadratic mesh too) that only uses 7 polygons (quads) and I'll LOL to the I'm-Sorry-I'm-Wrong-Bank."

I made an extruded pentagon with Moi and it did indeed have only 7 polygons. Probably a bit late to tell Distant Unicorn though.

PS Does anyone know of a page that will explain to me what I should be trying to achieve when exporting a mesh from Moi? Sometimes long triangles seem to cause problems and sort of pinching in places (mostly around holes) and to avoid this I try Ngons. Ngons make lovely smooth surfaces but confuse some programmes into adding extra surfaces. Its very puzzling and working neither in the computer or design industry I have no one to ask and few options for experiment.
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 From:  Michael Gibson
7616.14 In reply to 7616.13 
Hi Keith,

re:
> Does anyone know of a page that will explain to me what I should be trying to
> achieve when exporting a mesh from Moi?

I don't know of a page for that, but I can tell you that there isn't just a single answer because it depends on what you are trying to do with the mesh and what program you are importing it into.

For example if you're going to be sculpting the mesh in ZBrush adding little pits and bumps onto it, you will be looking for a different style of mesh than if you're rendering it.

If you could give more details about what you want to do with the mesh, what program you're trying to bring it into, and what file format you're currently using, that might help me to give you some advice.

- Michael
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 From:  bemfarmer
7616.15 In reply to 7616.13 
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 From:  keith1961
7616.16 In reply to 7616.14 
Hi Michael
I think I don't fully understand the basic concepts that others here have been taught or have learned through having a job that involves modeling in some way. I work in mental health services and consequently understand a lot of stuff that other people don't ever need to know about health regulation so I understand that when you guys discuss things there is an implicit understanding and a language that I will struggle with. My simplistic idea for a retirement hobby was to do something artistic; so making props for DAZ or selling models on Renderosity seemed a possibility. I'm ambivalent about the selling aspect as I don't actually need the money but on the other hand I do want to make things good enough to sell. After that I might just give them away:)

The problem I am grappling with (and its unfair to share this with you I know) is that Moi to Polymesh or Quads > Texture> Render is quite tricky and at every point there is a steep learning curb. To me most of the attached pictures have things that I didn't expect to see and it upsets the perfectionist in me. Not because there is anything wrong with Moi (its amazing) but because I can't work out how to correct them, or indeed tell if they need correction. They are as they appear in Blender, Carrara and Moi.
Keith
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 From:  Michael Gibson
7616.17 In reply to 7616.16 
Hi Keith, so in order to get a smooth render, there is a piece of information that is part of the mesh called "vertex normals" which is important to get used in order to avoid shading artifacts.

Unfortunately I seem to remember that in recent versions of Carrara they stopped reading in this information and without the vertex normals being used you will tend to get shading artifacts like you show. I don't think it used to be a problem so it's something that they changed in Carrara at some point and after that change it is not very good for rendering CAD data anymore unfortunately.

If you can find any import options for the Carrara import, see if there is anything labeled "Vertex normals" which you can enable, which would then likely solve the problem.

Blender has also had the same problem but I think it may be fixed up in the most recent version of that. I'm not entirely sure though.

Pretty much every other rendering program than those 2 will work better. You might try the demo version of Simlab composer and see if that works better for you.

For all 3 of these programs (Blender, Carrara, and Simlab composer) you would want to use OBJ format for saving out from MoI, with Output : "Quads and Triangles".

But I think it's likely that if you try a different rendering program that does support reading vertex normals from the .obj file that would get you higher quality shading and avoid those problems.

- Michael
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 From:  chippwalters
7616.18 
Hi Keith,

Hopefully this will help a bit. Consider the below image:

PIC 1

At the default Mesh Option settings with an Angle of 12 (dot 1), you can see there are lots of large triangles on curved surfaces, which when rendered ABSOLUTELY WILL cause artifacts using any polygon renderer. The angle determines how and when to break up curved surfaces. As you can see (2) the surface outline is most facetted, which won't look good unless you are creating a very small render or building for games. This setting creates a very small model size (3), only 34K polys.

PIC 2

By just decreasing the angle (4), we can create more polys along the curve (5), which will render somewhat better. But we still have those pesky triangles and it would be nice if we could raise the number of polys on the longer curves (5). Note decreasing the angle increased the file size to 106K polys.

PIC 3

So, to get rid of the long problem triangles, we typically need to fiddle with the Divide larger than number. Here we've set it to .2 (dot 7) which means any polygon larger than .2 units on any size will automatically be divided. Wow it's very smooth! (8) We set the dropdown to All, but we could also set it to Curved since there aren't any flat planes in this model. As a rule, I typically set it to All unless either a) the geometry is regular (boxes w/out slow curved surfaces); or b) I want to use micro-beveling in KeyShot (which doesn't work well with small flat polys on the same plane). This setting turns out is overkill for this model and the poly count is up to a whopping 182K! More polys = longer renders and slower performance ;-)

PIC 4

This is a pretty good setting for this model to be rendered at a fairly high quality. The Divide larger than is set to .5 (dot 10) and the model should be exported as OBJ and import fairly well into most rendering packages. Fairly decent curve resolution (11) and a poly count of 120K.


The exported OBJ can be found here.

EDITED: 17 Sep 2015 by CHIPPWALTERS

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 From:  keith1961
7616.19 In reply to 7616.18 
Thank you both for your help. I know that Michael has been patent enough to explain about Carrara and normal before so I am Doubly grateful this time. Chipp that was a great pictorial explanation too. The model I copied on turbo squid http://www.turbosquid.com/3d-models/3d-model-cartoon-crab/822724 has only 5,646 polygons and looks very smooth. Do you think the problems I am having are to do with the software I am using rather than the models I produce? I think my modeling is getting better but my renders are disappointing.
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 From:  Michael Gibson
7616.20 In reply to 7616.19 
Hi Keith - yes I do indeed think that the particular problems you were indicating are due to limits in the rendering software that you're using.

The specific problem is that it's easy to get glitches exactly like you show if a particular piece of data called "vertex normals" is not loaded from the polygon mesh file and used to shade the object.

The 2 renderers that you are using (Carrara and Blender) happen to be about the only 2 ones that have this problem. In the past Carrara did not have this problem but apparently they've changed stuff in it in more recent versions that has introduced this problem and made it problematic to use for rendering CAD data. I seem to remember that very recently this may have been solved in Blender but I'm not completely sure about that.

I'd recommend saving your model as an .obj file out from MoI using the option for "Output: Quads & Triangles" and then loading it into SimLab composer and see if that gives you a better looking smooth shading. You can get a trial version of Simlab composer here:
http://www.simlab-soft.com/3d-products/simlab-composer-trial.aspx

Also if you want smoother looking results, moving the slider a little bit to the right to increase the number of polygons created can also help with that, like Chipp shows above.

But the key thing to get a good looking render without shading glitches is to make sure that the vertex normals smoothing information in the .obj file is being loaded and used by the renderer - apparently Carrara is not doing that anymore and so that will lead to shading glitches exactly like the ones that you have been showing that you want to avoid.

- Michael
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