Dear Agony Aunts,

Are my normals normal?
I'm worried that my normals may be abnormal, and that this may adversely affect my chances. I know this sweet little Fairy, and I'm trying to make some butterfly wings for her, but my normals don't look normal, and I'm worried that she will reject the wings, and me along with them. Dear Agony Aunt, can you suggest something to help me please?

This is a flat two-sided rectangle, and has groups for left and right sides. It has one material zone, with the mapping on the back side being a mirror of that on the front.

In the image both wings have been  morphed so that they bend forwards (see outline view). The left wing (your right) looks like it is bending backwards, but it's not, it's bending forwards like the right wing. This looks like a classic case of reversed normals, right? But is it? If I import another instance of the prop with flipped normals the problem should change to the opposite side, yes? Here is the really weird part, it doesn't, it looks exactly the same as the un-flipped version :huh:! So perhaps it's not flipped normals causing the problem. But if it's not flipped normals what can it possibly be? :blink:

The problem only seems to be in preview, a rendered image looks OK. Is there any acid test to determine if the normals are actually facing out or not?

Dear Agony Aunts, I'm hoping you can suggest a way to fix the wings, so my Fairy won't forsake me.

P.S.
If that's not possible, I wonder if you could please recommend some quick acting poison? :sad:

P.P.S.

I'm using P6, and there is a transparency map applied to the prop.
 

Here is a side by side of un-flipped and flipped versions. :blink:

He, he, he. It's a Preview rendering problem.

You are using a two-sided mesh, so you have a front face and a back face. The vertices are not weldedand so each face has its own set of vertices.

During the rendering process the render engine must decide which face have to render. The faces that have the normal looking forward are rendered, but for each point there are always two faces with forward normals in the overlaping region and the renderer is picking the wrong face. The renderer seams to be biased and not symetric, in one side picks the right face and in the other side the wrong face. It also looks as the distance of the faces are not used for the decision of picking the correct face (No Z-buffer ???)

Inverting the normals of the mesh solve nothing, the distance between the front and back face is very small.

In the final render there is no problem, the renderer always render the correct face

Yes, probably the normals. This happens for me usually when i create a symmetrical mesh by copying one half, and then mirroring it. That way the face orientation of the mirrored vertices changes from inside to outside and vice versa. Practically nothing helps. When importing the double defined polygons, poser cannot distinguish which is outside and which one is inside, so it has to guess (and usually it guesses wrong). That leaves essentially two possibilities of what you can do:

Either give the model some thickness, and then, when importing the model, select "make normals consistent" and hope that poser gets this right or,

somehow change the face orientation for the wrong faces in your modeling application (must be counter-clockwise for polygons visible from the outside).

(Note that for the rendering, you do not need to have those double sided polygons, you could simply check "normals forward" in the PoserSurface node).

PS. The normals of your morphed wing have nothing wrong, it are correct at every point. 

Thanks everyone. It would have been nice to find a solution, other than redoing the mesh as a solid. But as it seems OK when rendered, I guess I will just have to live with it. At least it is not something I did wrong.

I really appreciate the explanation, and that people took the time to check out the obj. So thanks again folks!

Try to sepparate a little the front and back planes and then morh again.

That's a very beautiful butterfly!

Quote - That's a very beautiful butterfly!

The texture map is a slightly tweaked photo of a real butterfly. And yes, it is very beautuful!  :)