Mesh Structure, Supportive Edges, Edge Flow
Basics of topology in 3D modeling

Let´s talk a bit about topology guys. But first, I would like to give a quick thanks to everyone who joined our Discord. Your questions really helped shape this post.

If you would like to join, just follow this link.

Alright, jumping into the topic. How to understand topology in 3D modeling?

When we talk about the topology in 3D, we are referring to edge distribution throughout the model. To demonstrate an example, have you ever asked yourself any of the following questions?

  • How do I know that my edges have proper flow?
  • How do I know if I have even distribution of edges in my mesh?
  • How do I know if my mesh is clean?
  • How do I see if there is pinching?
  • Why does my subdivided mesh look so deformed?

All of these questions are based on topology, e.g. how edges are organized on any given model.

But are there rules or a workflow that is easy enough to understand, so we can apply it every time we approach a new project?
Well yes… and no. There are very easy rules to remember,  but learning to apply these rules properly do different meshes, will require a lot of practice.

Where to begin?

So what is the proper topology in 3D modeling?
Let me first show you a few examples where topology became problematic, and then let´s see if we can find an easy solution to the problem.

In this example, we can see that there is some distortion on the mesh. But we already know, the closer two edges are to one another, the sharper the area.

So why is this happening?

We can clearly see that corners in the yellow highlighted area are forming a sharper corner right?

While it is true that two close edges will give a sharper corner, there might be some deformation if those same edges are super close on one end, and widely spread on the other.

Like we see in an example above, a wide edge spread area on the left, is gradually flowing into a narrow edge spread area on the right (highlighted yellow). The transition between these two areas of the mesh, where we have a big empty area with no edges will cause deformation. There is simply not enough geometry there to support that structure.

In order to avoid the problem, we would need more edges to release some of that tension.
So what would be the easiest fix for this problem?
The answer is, create more of an even edge spread (or edge distribution). While adding new edges, we need to be sure that our edge spread is even and looking like squares. Also known as quads.

Much better! Ok, so now we know we need an even spread of edges to avoid distortion. But even spread alone is not enough. If the spread number (or poly count) is too low, we might encounter the same issue later when we need more geometry for details. So what do we need to avoid this type of distortion?

We need even edge distribution that is not too dense or not too widespread.

There are positive and negative sides to manipulating edges in both low and high poly (edge) count. Let´s see what they are.

Low poly count

The positive: Low poly count will enable us to easily modify the shape and block the idea out.
The negative: We can not establish details with a low poly count. The more details we want, the more geometry we will need.

High poly count

The positive: With larger polycount, we easily can add more details, and easily tighten the mesh.
The negative: On the other hand, larger polycount meshes are harder to control because there are more points and edges to manipulate.

So, if we summarize this information, what would be a conclusion or the rule we would apply to our workflow?

Rules to follow so far

1. We need to start very low poly.
Why? Because the mesh is easier to control and helps us establish our shape faster.

 

2. We need to make sure to have even edge distribution.
Why? Because we want to be sure we have enough geometry for our details and sharp corners. Uneven edge spread can lead to unwanted results as we´ve seen in our first example.

Great! Two simple rules to begin with. Not so hard to remember right? But is that all?
Nope… we have two more. If we now check our progress, what would be our next step? Our last example shows that geometry has no distortions due to evenly spread edges, but now the corners are no longer sharp.
In order to do that properly, we need to get ourselves familiar with supportive edges and edge flow. Let´s do that next.

Supportive Edges

What is a supportive edge?
Supportive edge will simply make sure that your object maintains sharpness once the subdivision is applied.
Any edge/shape we wish to tighten will need at least one or two (recommended) supportive edges. Usually, that is the outline of our model. Two edges close together will form a sharp corner. We just need to follow this rule.

So in our example, where would we position our supportive edge?  We previously mentioned the outline, right?
If that is the case we can either extrude the outline edges (shown yellow) outside or duplicate the edge on the inside. And that is how we set a supportive edge.

Once the shape is extruded, the outline edge should ideally be surrounded by 2 supportive edges.

Now we can quickly check how our mesh would look like if we apply subdivision. It looks ok, and it appears there is no distortion on the surface once we bend it. Good enough so far.

Let’s add supportive edges to our rules list as well.

Rules to follow so far

1. We need to start very low poly.
Why? Because the mesh is easier to control and helps us establish our shape faster.

 

2. We need to make sure to have even edge distribution.
Why? Because we want to be sure we have enough geometry for our details and sharp corners. Uneven edge spread can lead to unwanted results as we´ve seen in our first example.

 

3. We need to add supportive edges.
Why? Because supportive edges will make sure our main shape (or outline) keeps its structure once we apply subdivision.

Edge Flow

What is edge flow, and what is edge redirection?

In many situations, our first three steps will not always give us the result we want. Some corners might not be as sharp or soft as we want them.

In our case, all of the corners are still very soft, instead of sharp and crisp.

Now we need a way to manipulate the topology we already have to get results we want, right? But not just that, we also need to keep our topology clean while maintaining quads.

If this area sounds a bit confusing, it just takes practice. More examples you go through, more it will become clear.

 

Let´s talk redirection first. We can start from our supportive edges, as they provide enough geometry to form a sharp corner.

If we go back to the very basics, we would have two examples. One example will have a soft corner and the other will have more shaper corner. Notice the difference?

So based on the example above, let´s go ahead and apply sharp corners using supportive edges where we can.

Now we are slowly closing into our final shape, and as you can notice there are only two more corners to sharpen.

Here is what we´re going to do. We need to rearrange our edges in a way so that they have a “gravity flow”. Say whaaaaat??

Yeah, its a thing that helped me understand this edges thing a bit better so hopefully, it will help someone else as well.

 

In the example below, we can see our current edge flow on the left. But now let´s check example in the middle.

We have a gray outline which represents our supportive edge. Now let´s also pretend that there is gravity force there, and depending on which angle we would walk on, that would be the flow for the edge (shown yellow). We just need to apply this logic to rearrange the edges, so they work in favor of the shape.

In the example on the right, I now removed the edges that we do not need, so we have more room to follow the “gravity” of our shape.

Ok, our original mesh is positioned left. Then, as shown in the middle, we would remove edges we do not need and organize the flow of the ones that do not match the “gravity” flow. Then, as shown in the example on the right, we would bring back the edges to the mid areas, to make all edges more or less evenly spread out once more.

This would be it guys! There are multiple other variations on how you could tackle this, but I tried to keep it straight simple and to the point.

Let´s just break down the rules one more time now that we are done.

Rules to follow on topology in 3D modeling

1. We need to start very low poly.
Why? Because the mesh is easier to control and helps us establish our shape faster.

 

2. We need to make sure to have even edge distribution.
Why? Because we want to be sure we have enough geometry for our details and sharp corners. Uneven edge spread can lead to unwanted results as we´ve seen in our first example.

 

3. We need to add supportive edges.
Why? Because supportive edges will make sure our main shape (or outline) keeps its structure once we apply subdivision.

 

4. We need to check if our edge flow is correct.
Why? Because different edge flows will give different results on the subdivision. This part will take practice.

NOTE: While these can be simple rules to follow, some factors may vary. For example, supportive edges can be added later, after you manage your edge flow. But it is a good practice to get to know the rules first, later the same rules can easily be broken and manipulated to match your work style.

3D Modeling Mentorship Workshop

Guys if you´re still struggling with understanding the basics of topology, we will hold another workshop in August.

We will go through a lot of similar cases, with more examples of what could go wrong and how to fix it. This is 1 on 1 training, so I´ll be with you every step of the way.

 

Here are some of the topics:

  • What is topology in theory and practice?
  • How to handle edges and their behavior flows in SubD modeling.
  • How to handle and avoid common mistakes like pinching and distortions in meshes.
  • How to avoid but also fix bad geometry.
  • How to approach complex and advanced meshes.
  • How to make block-out of your ideas.
  • How to progress through design, 2 method approach.
  • What is the difference between concept and production mesh?
  • How to fix but also transition from concept mesh to production mesh.
  • How and when to add surface detail and microdetails.
CHECK THE WORKSHOP

That is all guys!

I would be interested in hearing your opinion. If you have anything to add, something was still confusing and how are you liking this post format. I could do more article type content so feel free to let me know your thoughts.

Have a nice day!

-Mario

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