Duplicating, -scale, Normals, Reverse = Black Surface

[joaomontenegro]

grrrr, very anoying, frustrating problem.

First of all I only have this problem when Two Sided Lighting is on..do I need to have this on for rendering purposes?

ok here is the problem...

I have inherited a model and I am in the process of cleaning it up. Whoever modeled it used alot of instances which I am getting rid of and replacing with normal geo.

Once I have cleaned and fixed up one group of geo - it is all prefect, working fine. I then duplicate and scale in it the negitive to mirror it. I get the normal message - something to the effect of - be careful when you do this somethings may reverse, which they do. Here is where the trouble starts. With two sided lighting I get a black side (outer - the wrong side) so I reverse the normals but ths does not fix it. The camea facing geo is still black. In fact both sides are now black....and they render this way as well.

Now one fix for this is "Set to Face" which I used to do for this problem. Unfortunatly this hardens the polygons, leaving them unsmooth. If I then go and soften them, my surface looks terrible.

So yea, thats my problem....Its driving me crazy...If anyone knows a work around to this it would be great....

Thanks,

LR

[gwelch]

Try "unlocking" your normals in the set vertex normal dialog instead of setting the normals to each face, that has worked in the past with this kind of trouble, but not always.

[joojaa]

// Warning: Freeze transform with negative scale will set the 'opposite' attribute for these nodes: pCubeShape3 //

yes you must be sure to chek your Modify->Freeze Transformations [optionbox], the settings window normals option if OFF. Now if you freeze with normals on your bringing this about for you even very long way after the fact down the line in your history or deleted history.

Freeze is not that tool for beginners its far more destructivbve themn most of you imagenie if used carelessly.

[joaomontenegro]

Hi Guys, thanks for taking the time to respond. Unfortunatly niether suggestion makes a differnce. Very weird...I have never seen anything like this before...

Thanks again,,

LR

[drblacksnake]

post a small piece of geometry and camera in zipped MA file.

[joojaa]

It cant be reversed. once it happens it happens, you can only rebuild all normals again. No amount of fiddling will bring tehm bacck if you deleted history.

The advice is only so you know hoew to avvoid it in future.

[user_deleted]

There's is a trick to solve this kind of normals messup :
export the object in OBJ (in the options uncheck all possible buttons - no normals -no smooth - no group) and reimport.
This usually works, although you may lose your original textures (which you can reapply as the shading groups stays, just the OBJ recreates default shaders for each ...)

Good luck,
Guyb.

[joojaa]

or you can set normals to face but still ist screws up your uvs spo they need to be rebuilt!

[user_deleted]

As LoneRanger mentionned, in some case even "Set normals to face", delete history, then smooth, doesn't work as the normals are screwed up somewhere deeper ... never understood where though .... Had banged my head several times on this problem ...
Guyb.

[joojaa]

But then that means its not freeze normals screwup snce that fixes itself by setting to face!

[joaomontenegro]

wow you guys are awesome! thanks so much for taking the time to get into this and me out. I can't claim to undersand what started the chain of events that lead to this very strange/anoying problem, as lke I said I inherited these files. However, after much headbanging against the desk, guy_iti suggestion of exporting them as OBJ's then reimporting them has worked!!

Many thanks to all!!

LR

[crashmankurt]

When you duplicate an object, scale it in the negative direction and then freeze its transforms, it reverses its normals and the other thing that it does that is not so apparent, is it sets a checkmark in the objects render stats called "opposite".

I tackled this problem when making stereolithographs for a 3D printer. (for a 3D printer to print correctly, all normals and faces have to be set facing out.)

Never tried the object import/export trick, but to fix it in Maya freeze its transformations after mirroring it, reverse its normals and also uncheck the box that says "opposite" in the render stats of the object. To see if it worked, turn on Backface culling so it wont show any backfaces and turn on normals display, and you should see a fresh piece of mesh.

[user_deleted]

Huummm,
thanks for your answer, but I just wanted to mention that the question was from February ... 2006, in case you didn't noticed.

Cheers,
Guyb