Smoothing groups problem (low-poly helicopter)

MELKIY

I'm working on this ka-52...



...and, since it's a low-poly model, I made a little bit of optimization that resulted in small smoothing groups issues:

1) on the bottom in the places where one vertex connects a lot of edges



2) in and around this notch



The question is, how to avoid these problems in case of using smoothing groups for low-poly models? Should I have used different approach (i.e. making a high-poly without geometry issues for baking normal map) or this is ok for low-poly (I know that it's not, but still) or I miss some obvious technique? What is your opinion?

P.S. Also wanna hear critique about this model in general because I am new to 3d modeling and I should know as much as it possible mistakes that I've made.

james01

When you made the groove by cutting it out manually, the surrounding vertices of the groove were moved to a different angle.
Thus the reason for the smoothing/shading errors.
There are a couple of things you can do, all of which are trial by error:

Select the vertices individually and move them manually so they match the same angle.
As you move them you will notice the shading change.

or

Go back to an earlier version of the model that didn't have the groove, and then make the groove using a boolean operation.
By using a boolean for the cut it will be more exact.
Once the cut out area is removed, the surrounding vertices should be at the same angle.

or

Create an additional loop around the the grooves circumference which will minimize the shading -slightly.

or

Create a high poly model and bake a normal map. The shading errors on the low res model may still be there, but when the normal map is applied it should no longer be noticeable. Largely depenadant on the quality of the bake and your cage.

MELKIY

james01 wrote: »

Select the vertices individually and move them manually so they match the same angle.
As you move them you will notice the shading change.

You mean the normals of vertices?

Eric Chadwick

You can try editing the vertex normals to fix this area.
http://wiki.polycount.com/wiki/Vertex_normal

It is likely you will need to edit the normals, plus also move the positions some, plus add a few new edges. Edited normals alone will probably not hide all the smoothing issues, because the normals are basically interpolated in the viewport using linear gradients (look up Gouraud shading).

These smoothing errors are fairly minor though. They will not be very visible if the model is being textured, which most models are.

A normal map baked from a high-poly model can hide these errors, but the baker and renderer must use the same tangent basis.
http://wiki.polycount.com/wiki/Normal_Map_Technical_Details

MELKIY

Eric Chadwick wrote: »

plus add a few new edges

Could you show on my model where I can add those edges, please? Because I barely can understand how can it help.

Eric Chadwick

It's different for each model, because the topology affects the smoothing. You need to experiment.

james01 made several good suggestions, the third one is probably what's needed in your case. You may be able to get away with less vertices/edges than a full loop.

We have some pics and explanations here.
http://wiki.polycount.com/wiki/Vertex_normal#Smoother_Shading

MELKIY

Thank you guys. I used editing normals method and seems like all issues are now gone (at least big ones) plus it gave more flatness to the bottom.


Little advice. You should add all your supporting edges/chamfers/etc and apply smoothing groups before adding Edit Normals modifier coz there can appear excess normals that will mess your smoothing up.

Elrinion

Very nice model. Just want to add that sometimes the smoothing errors can appear because of non connected vertices. So always check if everything is properly merged.

Keep up the good work. o/

a3D

It might be caused by nonplanar quads. Moving the vertex normal manually does indeed fix the problem, but sometimes you can even prevent it in the modeling phase.

MELKIY

I've got a new problem. After unwrapping a model my edited normals disappeared. They work if I go back down to Editable Poly modifier,

but disappear again after going to upper UnwrapUVW modifier

I just want MAX leave dem normals alone! So guys, please, tell me what to do.

Eric Chadwick

Try adding a Edit Poly modifier on top, then Collapse the stack. (save first!)

It might be that UVW Unwrap is converting to Editable Mesh internally somehow. Or it could be you need to use Reset Xform, not sure.

Some more info here about preserving edited normals. Not exactly your situation, but might be useful nonetheless.
http://wiki.polycount.com/wiki/VertexNormal#3ds_Max

MELKIY

Eric Chadwick wrote: »

Try adding a Edit Poly modifier on top, then Collapse the stack. (save first!)

Didn't work. Edit Poly modifier resets normals itself.

What I found out:
If I select model with edited normals and go down to Editable Poly and then up to upper Unwrap UVW normals stay edited:

But when I unselect object:

Gonna learn more about xForm.

Eric Chadwick

Probably the result of using multiple Unwrap modifiers, plus an instanced Unwrap at the top. This is totally overkill, and will likely result it other problems.

It is best to keep the modifier stack as simple as possible. Many modifiers (like Unwrap) are dependent on the topology coming up the stack from below... if you change the vertex count in Editable Poly, those Unwraps will all be reset, because the vertex count has changed.

Best to use one Unwrap modifier at a time, and Collapse fairly often.

Obscura

If custom normals gets reset by collapsing and stuff, then maybe you should edit them only at the very end :P

Also "It is best to keep the modifier stack as simple as possible. Many modifiers (like Unwrap) are dependent on the topology coming up the stack from below... if you change the vertex count in Editable Poly, those Unwraps will all be reset, because the vertex count has changed.

Best to use one Unwrap modifier at a time, and Collapse fairly often." <-- this is very true.

Eric Chadwick

One way to salvage your work... in the top Unwrap, use the Save button to export the UVs to a file. Delete all the Unwrap modifiers. Reset Xform, and Collapse to Editable Poly. Add a new Unwrap and load your saved file. Collapse, see if the normals are preserved.

MELKIY

Thank you guys. Yeah, the problem really was caused by multiple unwrap modifiers. I collapsed dem all on every object (to avoid other problems) and added one to them all so pretty every object's stack looks like
-Unwrap UVW
-Editable poly.
P.S. Woo, gonna texture!

MELKIY

The other problem have appeared.
When texturing I use alpha channel as a selection and then painting over it to have nice neat texture. But after applying this albedo/diffuse map to the model these wierd seams appear:

Albedo looks like this:

So I understand that I should paint out of alpha channel edge to solve this problem but the question is: is there any another more elegant way to expand edges of selection?

a3D

MELKIY wrote: »

is there any another more elegant way to expand edges of selection?

Not really, padding is necessary, especially for mipmapping.

In Photoshop you can expand your selection/mask by a given number of pixels.

MELKIY

Just noticed that marmoset retriangulated my .obj file. Here how it looks in 3ds max:

and this in marmoset:

How to avoid this?

Obscura

Triangulate in Max before export. Add "turn to poly" modifier, enable limit, and adjust it to 3, and collapse. Then it will get exported with the triangulation from Max.

MELKIY

Thank you, Obscura. Yes, this method seems working but again it ends up with reseting my normals and editing them again.To be honest did't do that and left my model how it is. By the way here it is all textured:










Don't think that I'm gonna do something else with this so I can say that it is my fisrt serious model. The major problem is this is a bit too lowpoly and modeled without baking normals map from high poly. What issues else does this model have in your opinion, guys? Wanna hear critique if you don't mind.

AND, speaking of baking normals, could some one help with baking normals to a BOX. Yes Box. I just cannot understand what I am doing wrong.
First of all I make simple box in 3ds max. Then I clone it in the exact same position. Next I chamfer all edges in a clone box and apply smoothing group 1 to all faces. All the faces of the box I add to the SG 1 too. After that unwrap UVs on the low poly box (I tried unwrapping it with default box unwrapper, splitting all faces and by making seams and unwrapping box as one UV piece). Open Render to texture, enable projection, choose high poly, push cage a little bit - all the standart steps. But after applying baked normal map to my low poly box the bloody seams appear (I render in marmoset). If I render it in max the result looks like this: