Fundamental Flaws in 3D modeling or is it me?

#1

You will call me crazy at the end of this post, but I don’t think I’m wrong.

Intro: I’m brand new to any kind of modeling, but I’m not new to software. I developed some very known sophisticated trading systems for banks, and other stuff, so bare with me here. I’m recreating an aircraft in 3ds max 2016. So far it’s the most detailed recreation ever and things are going great except 1 fundamental problem I can not seem to understand.

The problem: Everything is fine with modeling except building/extruding/extending parts on a rounded surface (fuselage). The fuselage is a simple cylinder with 68 sides. Anytime I put a vert/edge on the surface of the cylinder, the cylinder changes the shading. 3ds Max assumes I am simply adding sides to the cylinder. This prevents me from adding any kind of topography in between the side edges. 3ds Max does not understand the difference between “drawing” on the side of the cylinder vs adding a side to the cylinder. Or maybe I am simply missing something. You be the judge.

It seems the topography is meaningless in my case. I literary tried everything and I learned to hide those problems by “drawing” counter lines to hide the errors, but there are cases where I can not hide it. Obliviously on flat surfaces this is not a problem at all. This is only a problem on cylinders.

Below are the photos of the problem. Please ignore the topology as finishing off those verts does not change anything. It will make it worse. Also, new users can only upload 1 image, so I will need to create multiple replies for the images.

problem
problem.png840x602 68.3 KB

Even with perfect topology adding 1 vert or 1 edge deforms the shading. I don’t know of a way to fix it.
3ds Max simply takes my verts on the surface of the cylinder and tries to turn the cylinder into a circle.

Please help, this is the only thing standing in my way.

#2

The smoothing that 3D software applies is a render effect and the visual is similar to what you would get if you use subdivision, so adding an edge there is like what you would do to try and make an edge sharper. There’s a lot of techniques to avoid issues like that, for example some careful planning can get the natural loops and edges to the place that you want. Increasing the number of edges on the cylindrical shape will also help to get a loop closer to the position that you want which will maintain the distance between the edges and avoid pinching.

Another technique that helps is to make a highly smooth base mesh and then use retopology tools to model onto the smooth surface to where it will match the curve. In 3ds Max those tools are under the Freeform modeling tab. You can set a mesh to model on and then create polygons and move things around on their surface.

#3

The outcome:
outcome

#4

Just curious, is your initial question answered? If not i will try to make it a bit more clear.

This all has to do with the normals. The blue lines are our normals here. The red curve will show you the resulting shading.

With just two adjacent faces the normals are like this. And when you apply smooth shading then the smoothing curve is at the right side equal at the left side. The surface looks smooth.

smooth1

When you divide one of the faces, then the normals looks like this. The smoothing curve is now at the one side much shorter than at the other side. And then you get a different shading here. And the closer the new created edge is at the center, the sharper looks the edge.

smooth2

#5

I’m unclear what you’re trying to do here, whether extruding the indicated region via your posted image or simply ‘drawing’ over the cylinder’s surface?

#6

And here’s also a comparison on what I was talking about–making a completely smooth shape and using the modeling tools where it will snap to the surface of the smooth model.

modelingcomparison
modelingcomparison.jpg2400x520 467 KB

#7

That’s a very nice illustration of what is happening in that circumstance. And it’s entirely logical. if the new edge were pulled out along its own normal in keeping with the red curve that shading artifact would be fixed - or at least moved into the adjacent polygons.

#9

And here is continuation of the problem. I detached 12 perfect polygons from the fuselage and now I have another shading bug even though the verts are in the same location. If I reattach and reweld everything goes back to normal. I need that part detached as it’s a moving part.

I would not mind the part to be shaded different, but look carefully. The shading changed at the bottom and at the top the most making it completely unnatural and just outright wrong.

detached

#12

Just to be clear, obviously I am the fool in all this. I chose to do something with a tool that is not a precision based tool. Now all my energy goes into fighting the tool. I maybe used 5% of the tool to create this project, but I am totally disappointed with it.

Just so you know I already have 68 edges for that main cylinder. That is high. I can not use or ever would Turbosmooth or anything like that in 3ds MAX. This is more of a serious gaming project than simply 3d modeling.

#13

Well, I’m building an airplane for a simulator. Must be perfect. I decided to recreate parts in 3ds max that others recreate with Photoshop and illusion. So for example, if there is a flange or any sticking part from the fuselage I simply extrude that from the fuselage. In this case I am doing an air brake which is big and it spans multiple edges in my cylinder.

More, the air brake has to be detached as a separate part and it has to move. Seems simple, but there are rounded parts on a rounded cylinder. That’s when it gets complicated especially when detached. I was able to get this far because the parts were either smaller, or I would hide the problems, or I would build a separate object and simply placed it in the required location.

I was aware of that cylinder shading problem from almost the beginning, but it never blew up until I hit a complicated part that is big and I can’t hide the problems.

Thanks guys for your time.

#14

It’s not a bug, polygonal modeling is supposed to work like that. Tiles is right, your problem depends on normals. I am talking about vertex normals, not face normals. Face normals define the orientation of the face, vertex normal control the shading between faces. You can edit vertex normals of the added egde in order to compensate and correct the shading. I don’t remember if Max has a tool to edit them tough.

#15

%.02 : it looks like you are fighting the tools because you do not understand them well enough.

  1. smooth shading in the viewports is indeed an approximation of lighting, so gradients aren’t 100% correct - with that said, what you are objecting to is going to be a legitimate issue when you try rendering this with a real lighting system (real time or not)

  2. suggest reading up on mathematical principles of high-order surfaces such as NURBS or subdivision surfaces, at least to understand the principles of smooth derivatives and geometric continuity. Hopefully this will clear up many of the confusions in the posts above between the tessellation tools (smooth-preview, etc) and what the actual underlying surfaces are doing when you apply the various tools to them.

#16

What I’m talking about with my example is getting your edges in the right positions in the first place, rather than trying to put an edge in the middle of a curve you need it to flow with the rest of the topology. In my examples there’s the windows and doors which are all at different locations but they flow with the topology. The aircraft model I have there has a small polygon count and I’m using it in software right now for low-end computers and mobile.
The mesh that has all of the polygons is a temporary mesh that represents the fuselage without any details and allows me to model on top of it an whatever I put on top of it will match the curve.

#17

darthviper107, Yeah, you’re correct. Your model is a masterpiece comparing to mine, but let’s dive into the details:

Your lines are flowing and it’s low poly for sure, but look at the number of “sticking out” parts on my airplane. I was able to make it work till now, which has way more parts that are way more irregular than yours. So in theory I got much farther than you in terms of being able to make it work. I hit a problem with a bigger irregular detached part on a rounded surface.

Bare with me here, and I’ll show you more. Your model is zoomed out, from the front angle and from the top. I can take your model, put 2 verts on the side, flip it, zoom in, and show you the problem, no matter what kind of topography you have. That’s all because of the cylinder shading. You’re not wrong, but you’re not showing me what I’m asking for and we’re not comparing apples to apples.

Now, to show you I’m not just being difficult. I did what you told me. I took a simple part of the fuselage with good topography and Detached it. Here is the detached section with topography:

before
before.png1094x746 124 KB

#18

and here is the after effect:

after

I am sure I am doing something wrong, but look at the shading of that part carefully. It’s not consistent. The top and bottom has more “egile” shading. It makes it irregular and it makes it different from the main part even though nothing changed in terms of shape, position, topography or light.

Anyway, Like I said, I can’t fix 2 verts on a simple 12 sided cylinder, then I won’t be able to do it anywhere else, and no one was able to do it either.

darthviper107, the thing is all these problems don’t show if the “cut” is on top or bottom, but mostly on the middle of the cylinder, because that’s where the shading goes from light to dark.

#19

If what you saying is true and I can orient it, that solves all my problems. I have no idea where I can find this in 3ds Max 2016 though.

#20

Shehbahn, I am not confused about anything to be honest. I actually believe NURBS exists because poly modeling in 2019 is silly. I do understand the principles of subdivision and all that. I do understand Chakins “algo”, and I understand that averaging out problems across smaller parts makes it less visible to the human eye. I don’t agree with it for computer modeling. It maybe made sense in the 90’s. That theory and stuff is beautiful, but as the algo suggests, it “averages out”, but not necessary eliminates the problem. I’m interested in elimination of it. Thanks for the post, but I need a practical solution to fixing a simple cylinder shading problem, that so far no one was able to do or even reproduce it.

#21

oh, you are definitely confused :wink:
everybody used a lot of nurbs in vfx way before polygons, subdivision surfaces changed that (thank god). Nurbs still has its uses in product and automotive design/production.

your issue is normal related, believe it or not. (set your polygon smoothing angle lower than 10degrees and you get your flat shaded cylinder) …and btw. nobody stops you from using nurbs.

good luck!

#22

You’re definitely not understanding, the issue is that you’re trying to put an edge in the very middle of the face which is affecting the smoothing, you need to design the mesh so that the natural edges end up where you want to extrude your complex details.

The method I’m talking about is to use the Freeform modeling tools in 3ds Max to where you can model on top of a temporary high poly surface, you can make your details work with the topology to avoid smoothing issues.
The other thing you’ll need to learn about is smoothing groups, it’s in a section under Editable Poly/Edit Poly, and it controls which polygons are smoothed together

#23

With that example, turn on the display of the vertex normals if your software allows this. And you will see that it is indeed a normals problem.

Shading is calculated by the vertex normals.