When I lent my services to a collegue who was working on a film about 12 years ago, I was introduced to the world of cnc. I remember watching this huge machining centre milling out a slab of mdf and turning it into a fantastic set of gears. I knew that it would have taken me hours to achieve the same thing with traditional power tools. I decided then that I would invest in a cnc router for my own business Oxenham Design. At that time I could turn on a computer, but even to check email seemed like a crazy set of operations. I persevered and learned every piece of relevant software I could get my hands on. I am now fortunate enough to be using Vectric's ASPIRE software, and Techno cnc routers, which has helped us to create some amazing projects, both in part, or in full. I thought that this blog would be a great place to share "behind the scenes" adventures with the software, materials and equipment we use, as well as the projects we build.

Tuesday, 16 April 2013

subdivision surface (a basic overview)

Due to the TV show NDA, and I can't post anything, I'm going to do a small summary on SDS modelling. This is done in our modelor of choice, Hex. This does translate over to any SDS modelling program, like Silo, Blender, etc.
There really is no "only way" when it comes to 3d SDS modeling. There are general guidelines for animation and rigging, but as we generally model everything in our final pose, most of that doesn't quite apply for us.

The first thing is understanding what happens when you smooth an object:
Heres a cube in Hexagon, pretty straight forward! Until you smooth it:
With 2 levels of smoothing, the cube is now a sphere?!?!? This may surprise, or even discourage people from using mesh modelling, but it's completely expected behavior.

When smoothing is applied (which blends all the faces into smooth surfaces) a mathematical process is calculated.
Here's the same cube from the front view
With 1 level of smoothing applied, every polygon is divided by 4, then the edges, or 'vertex' are averaged between the polygon right next to it. This essentially starts to smooth the surface out.
If I apply 2 levels of smoothing, our 6 sided cube ends up with 96 faces (or sides) Once we understand that this happens consistently, every time, we can start to have an immense amount of control over how our shape comes out. This is why we want to try and keep as many faces of our shape as quads. This means a polygon with 4 edges. Quads smooth predictably, every time. Polygons with more, or less than 4 sides are unavoidable, but keeping them to a minimum, or hiding them deep in a model, keeps our results predictable!

The cube we started with is actually considered a low-polygon model, or low resolution.
We can strategically add vertex edges to the cube to get it to hold it's shape when we apply smoothing. Essentially we will be adding resolution to our cube.
If we add an edge loop very close to the edge of the cube, the distance the computer averages the polygons is drastically reduced.
You can see the results quite clearly. The ends where the edge loop has been added have held their shape a lot better. A tad bit soft, but not a sphere. Because we didn't add any edge loops on the other faces of the cube, they rounded right out.
Now, if we add a set of edge loops to the other edge of the cube, we'll be adding resolution in the other direction.
This is clearly a step in the right direction. It's a little bit weird on the other side, because we haven't added any resolution in that direction yet.
I've added resolution to the remaining sides of the cube.
Now when add smoothing to the cube, the tighter resolution holds it's shape a whole lot more.

You might be asking why we would smooth a cube, adding all of those faces, when we started with a cube in the first place. The truth is, if you need a cube, then use it the way it is. But if this cube was welded into another piece of geometry, then that new geometry was smoothed, the cube would go spherical again.
Our last image of the cube has the edges and corners looking a tiny bit soft. The closer we move our newly created edge loops to the edge of the cube, the tighter the corners will be.

This always is the case, always. The higher and tighter the resolution, the sharper the edges will be.

Tomorrow, I'll show you how to add a perfectly round hole into the center of a square. Easy when you know how it works, frustrating if you don't know. Hopefully these little blogs will inspire you to give SDS modelling a try. Or help with any trouble you may be having understanding how it works.
When I started, I just wanted to know what was happening, and my frustration level was through the roof!

No comments:

Post a Comment