Head Model Coordinates

Perfect generic models and UV mapping

There are five main stages I recommend for creating a photo-real, textured 3D model. They are: generic modeling; photography; UV mapping; detailed model fitting; and texture generation. You can group the four steps into two stages: generic modeling/UV mapping and detailed photography/texture baking/model refinement. The first two steps, generic modeling and UV mapping, are basic characteristics of a head model and are independent of any actual textures or detailed face morphology. This is what we will cover in this chapter. We will look at combining the photography, model refinement, and texture baking in the next chapter.

Generic modeling and UV mapping share many of the same goals: use quads for optimal subdivision; have smooth edge lines that follow the contours of the face; have even shaped and sized quads (maximum relaxation within the surface shape); and have detail where it is needed around the eyes and mouth. Ideally, your head shape and mapping are based on the average human mean shape so you can later plug it into a parametric head program to change its shape to any human head.

UV mapping involves generating mapping coordinates for each 3D vertex. As the 3D vertices have XYZ coordinates, the texture's coordinates are named UVW. While it is possible to paint totally in 3D and ignore all details of UV mapping, this is very inefficient. We need to pay the same attention to the quality of the UVW mapping as we did to the XYZ modeling.

All 3D models are broken down into triangles at render time. This is because a triangle is a minimum definition of a plane area. A triangle in 3D space can always be viewed flat-on for the purpose of placing a 2D texture on it. It's possible to convert any 3D shape, no matter how complex, into a flat shape by taking all the triangles and laying them out within a rectangle. So. no matter how complex a 3D surface is we can always cut up our texture into lots of separate triangles and pack these into a rectangular map for texturing. This will always work, but it's messy, wasteful of space, and creates lots of technical problems blending the edges of all those triangular texture pieces.

The goal is to come up with a minimum stretch, maximum connectivity mapping from 2D (UVW) space to 3D (XYZ) space. Ideally, the 3D mesh and 2D UV mesh have the same topology. There are a number of ways to approach this problem, but one of the most successful ways is pelt mapping. In this procedure, you think of the 3D model as a skin you want to cut open and stretch—like real-world pelting.

Finally, you want to consider the use of 2D texture and how it maps to your 3D model. As humans, we focus on the front of the face—the triangle between the eyes and mouth in particular. Your UV mapping should reflect this natural focus and give preference to this region.

Heads Humans

O Step 1 Mesh triangles

Q step 2: Efficiency ie ie<

eparately in UV space, but thi s ¡s vie hading difficulties. Here, I have focused 0n > that is already UV mapped I have broken °r'e w and pulled the resulting set of UV coordm^ see, this results in one 3D vertex requiring eioht n each triangle that touches that vertex. Ideally We v He per 3D vertex which we can only achieve if the UV marl' * it with the same topology (connectedness) as the 3D mesh 9

How Topology Human FaceFace Texture Map

Q) Step 3: Standard UV mapping

Every 3D system provides some basic ways of generating UV coordinates. For a face, spherical projection (with some squashing of the projection) does quite a good job. To get the best from spherical mapping, position the seam (green line in the gizmo) down the back of the head. Position the gizmo right between the ear holes and then scale it to fit the front of the face optimally.

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  • Cipriano
    How to topology human face?
    8 years ago

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