
	Eg 1: NURBS Surfacing

Figure 174. The Head Polymesh

A blank polymesh can be quite daunting to the beginner; where to start? In this example you'll learn only one of several ways to surface a human head, but the general approach taken can be used on any polymesh. The key is to first sketch out the main feature lines, then connect between these to create the regions, then these are filled with patches.

Stage 1: Preparing the Polymesh

Before rushing ahead with the surfacing process, make sure you have a clean polymesh. The patches fit to whatever you give them, so if your polymesh is rough, the final surface will be too.

Figure 175. Before Editing

Figure 175 shows the head polymesh before editing. If you compare it to the head at the top of the page:

(1)

The shoulders have been removed because they won't be surfaced. Making the polymesh as small as you can will help speed things up.

(2)

Holes around the chin, in the eyes, and on top of the head have been filled. Patches will not fit to empty space, so all holes in the polymesh that will be covered by the network are filled.

(3)

Roughness around the mouth, cause by a short beard, has been smoothed out. This will give a much better looking surface, and the short beard can be mapped on as a texture, or modeled with CG hair.

(4)

The ears and nose have been sculpted to fill in missing information. The original polymesh came from a 3D scan that didn't capture behind the ears or up the nose.

(5)

The mesh has been decimated from around 400k faces down to around 80k faces (i.e. reduced by 80%). This will speed up the network creation process, and the original polymesh can still be used to extract texture maps.

If you wish to work along with the example, then right click here to grab a ZIP file of the edited polymesh (859Kb). Note: To grab a binary file, first move the mouse pointer over the link, click the right mouse button, then select "Save Link As..." or "Save Target As...".

Stage 2: Drawing Feature Lines

You will get better results if you can get the patches to flow along major feature lines in the polymesh. The best way to ensure this is to start off by sketching some curves over these features.

Figure 176. Major Feature Lines

Figure 176 shows the beginning of this process for the head example. The edge of the ear is a major ridge that needs to be followed. We need a curve along the mouth split line; it'll become a patch boundary at some point. And some curves have been drawn around the eye and nostril and along the crease between the cheek and the nose/lip area.

Because heads are roughly symmetrical, we only need to work on one side in the initial stages. The patches fitted to one half can be mirrored and fit to the other half.

Figure 177. More Feature Lines

Figure 177 shows the completed feature curves. There's some more around the mouth and nose, one along the jaw line, and one that's the split line between the two symmetrical halves. Right click here to grab head-net1.zip (7k).

Stage 3: Major Flow Lines

The next step is to decide how you want the patches to flow over the surface. Typically for heads, especially when they need to be animated, the patches radiate out from the mouth.

Figure 178. Major Flow Lines

Figure 178 shows the major flow lines sketched out. As you can see, some of the feature lines have been modified or even deleted. The curves around the nostril have been simplified. The jaw line has been trimmed back and redirected to create the circular flow around the mouth. And the eye brow line has been extended to continue this circular flow.

No flow lines have been drawn around the back of the head. This part of the head is quite rigid, not changing during animation, so the patches don't need to flow in any particular way in that area.