Get started with subdivision modeling in Alias

00:02

In Alias, we can create smooth NURBS models

00:05

using subdivision modeling techniques.

00:09

A subdivision object has an orange wire frame

00:12

but sometimes it will be shown green if it's got construction history

00:15

like Symmetry Align here.

00:19

The individual patches are known as limit surfaces

00:22

and we don't manipulate these directly.

00:24

Instead we use the subdivision control cage

00:28

that I can show with this box shading mode

00:30

and manipulate by turning on the control vertices.

00:35

And then I can use the normal Selection and Transform tools

00:39

to shape the subdivision either in the box shading

00:42

or more typically with surface shading.

00:45

And you can see that all the limit surfaces update and stay connected and smooth.

00:51

And because these are NURBS surfaces, I can create a hybrid model.

00:56

So you can maintain the simplicity of the SubD control cage

01:00

but also use traditional NURBS trimming and surface tools.

01:05

So here I've projected curves and trimmed holes in the limit surfaces

01:09

and added a surface filet

01:11

and the same up here

01:13

all with history and without affecting or over-complicating the SubD topology.

01:19

So you can present a finished design but keep the subdivision model easy to change.

01:26

And the topology of the control cage is key

01:28

to sculpting more complex shapes like this car.

01:32

So we're generally aiming for quads where possible

01:35

with a good flow in both directions.

01:38

But we do have the flexibility with subdivisions to use star

01:41

points like these five edges coming into one point here,

01:45

and n-gons like this five sided one

01:48

and three sides down here.

01:51

And this thicker edge is a crease on the subdivision cage

01:55

which gives a sharp edge on the limit surfaces.

01:59

So if I check the G2 curvature continuity,

02:02

all the non-creased surfaces are smoothly connected.

02:06

And where a crease is specified, you get G0 position continuity.

02:13

You won't get production quality highlights,

02:15

but you do maintain a smooth coherent object as you make changes.

02:20

And this means that you can focus on shaping

02:22

your design by moving the control cage vertices.

02:26

And the subdivision math does all the work

02:28

of keeping those limit surfaces smooth and connected,

02:31

which is a big time-saver around tricky blended areas like this wheel arch.