PolyMerge blacking out half of model?

[seven6ty]

Help meeeeeeeeeeeeeeeeeeeeeeeeeeeeeee.

[Gremlin]

yea thats happened to me before... I dunno wtf, but setting normals to face seems to fix it (and then averaging or smoothin normals if u like a smoother look in the perspective) but I dunno--normals piss me off, I've modeled an ear and then found that somehow the normals were facing the right way so that when I tried to append it to my face it wasnt working properly...

anywho, yeah, just "set normals to face"

[ceql]

Yea, it's a problem with Normals.
It seems to be most potent when editing models imported as .obj's (Maya bug?)

imho the easiest way to fix all normal problems, is to just convert to subdivs and then back to polys again.

If you do it this way, Just make sure that you have the 'SubDiv->Poly' option set to 'Verticies', and that your model doesn't have any non-manifold faces, etc. (it's good modelling practice anyway [to avoid non-manifold faces when possible]) :thumbsup:

[* edited for clarity!]

[Emil3d]

... (it's good modelling practice anyway) ... Never heard of that before and I won’t recommend it. Successful Poly to Subdiv conversion requires very clean geometry. If you create a default poly primitive and reverse just one face, the object will fail to convert to subdiv.

For problems with normals I would recommend: first to display borders to check for shells or edges which are not merged and after you have the geometry as one continuous piece first display the normals and then select a face with the desired normal direction and use the Conform command.

[nurcc]

Ran into something similar a few days ago. It was something weird with the normal, where merging points would black out maybe 40% of the model. It was setting the normals of all those faces to the same thing. I tried set normals to the face normals, which worked fine, but if I merged points, the same problem happened again.

To fix it, I exported the poly as an obj - there's an option in the export to export normals or not. I turned that option off, and when I re-imported, the normals were set to the face normals, and merging no longer gave me problems.

[ceql]

Never heard of that before and I won’t recommend it. Successful Poly to Subdiv conversion requires very clean geometry. If you create a default poly primitive and reverse just one face, the object will fail to convert to subdiv.


That's why I said, if you're going to try this, to make sure that you don't have any non-manifold faces :bounce: (Which may mean doing a 'Conform' or a poly 'Cleanup' first, if the model isn't so clean.)

Sorry, I should have clarified that when I said "(it's good modelling practice anyway)" I was reffering only to avoiding non-manifold faces with regard to high-poly models, and my point there was only that having clean geometry (including surfaces which are all manifold) is good modelling practice.
A model with some stray flipped faces, like a sphere with a single flipped face, is non-manifold geometry, and generally isn't really a good idea for output that needs to be smoothed, especially since some implentations of SubDivision surfaces won't support them at all. (Maya's for instance. Not sure about Renderman sbs though?). That's why there's a Maya function specifically made for removing non-manifold faces. I can't really think of a situation where non-manifold geometry would be useful for highpoly stuff, though. Typically they're only there accidentally, and you won't find anyone recommending 'em, but please let me know if you know of any practical application for them, because I'd love to know :)

Of course, it may be a different ball game for realtime models though! :)

[I've added a note to my original post to clear any potential confusion!]



Anyways, opps, getting a lil bit off topic! :)

From personal experience only, I've found that converting to Subdiv and then back to polys works for me for when I want all soft normals on my model and when *occassionally* the usual combinations of 'Set to Face', 'Average Normals' and 'Soften/Harden' sometimes don't work. ...Or, even less occasionally, it does work but when you edit it more, the normals are instantly screwed up again (similar to what nurcc was reffering to). However, this only ever happens to me when I import/export .objs, and it's probably something small, like me not having set the proper export settings to accomodate (opps!). So, definetely consider try using it as a last resort if nothing else works, because it always works 100% for me. It's like the conversion seems to reconstruct the normals completely. But yes, you must have a clean model to do it this way!

Just use whatever works, I guess!

[seven6ty]

Thanks guys! Good explanations...

Although oddly enough when I re-openned Maya to combine my poly's and merge edges it worked this time! Grrrrr, Maya sometimes. Oh well. Odd shit.

But yeah, there's no stinkin non-manifold geometry on myyyy geometry, I know this shit! Hah, ehhh, excuse me, it's late. :-/

Thanks again though!

[rintintin]

Hi,

Your having problems with your vertex normals. If you check them by going to
Display/Custom polygon display and ticking Vertices/Normal
You should see that the black vertices have there normals pointing in odd directions.

There are tools within Maya so you dont have to merge models/export etc.

Goto Edit Polgons/Normals/Set Vertex Normal. Open up the options and make sure Unlock Normals is ticked and then apply. This will fix the problem. Maya lets you to edit the directions of vertex normals and to stop the edited normals from moving it locks them into position. By unlocking them you alow them to go back to a default position. Maya just gets a bit confused now and then when you build new polygons or attach poly pieces together.

Probably a good idea to have a play with the tools in this area to become familiar with them.

[meatpuppet]

i'm guessing that you duplicated half of your model, scaled it -1 along one axis and then combined the two meshes and merged vertices, correct?

scaling negativly flips the poly normals so they're facing inward and because they're flipped they display black (sometimes, i've seen it not happen though. it seems to also have something to do with graphics card/display issues. but also note reversed normals usually still render fine) anyway...

the best thing to do is:
1. duplicate mesh half
2. flip -1 along appropiate axis
3. reverse normals on the duplicated mesh
4. combine
5. merge vertices

this way you don't have to force the normals back to the correct direction with 'set to face' or something similar that could change your topology in an adverse way.

hope that helps,

[seven6ty]

Well I checked the normals on the faces, and they were all pointed out like they should be... You guys were talking about the vertex normals?!?!?! I didn't know that they had normals, if I'm understanding you correctly.

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