Inspired 3D: Character Modeling Tutorial (continued from page 3)

Initial Surface Alignment Tools
The alignment tools discussed here were used to create the initial surfaces. These tools take advantage of curve construction to create and maintain tangency when building surfaces from curves.

Align Curve
Align curve can be used to make existing curves have common end points, and have the end of the curves have continuity. The continuity options include positional, tangential or curvature continuity.

Project Tangent
Use project tangent to create smooth curve transitions where curves meet existing surfaces. Project tangent creates a tangency condition at the point where a curve coincides with the edge of a surface. First select a curve then the isoparm on the adjacent surface that you want the curve to line up with. Project tangent will also line up a curve with two adjacent curves to create a tangency condition. You cannot use project tangent to align a single curve to a single curve. The Align tool, which will be discussed later, will work for this.

[Figure 12] Patch surfaces created by splitting and rebuilding initial surfaces.
Surface Tangency Options
The square surface and the bi-rail surface provide options for tangency between surfaces that have been built and surfaces that are being built. These options operate on the surface boundaries. The square surface simply has one option that turns tangency construction on for all boundaries. The bi-rail surface has options that turn tangency on for the first profile, the last profile or both first and last profiles.

Separate Initial Surfaces into Patches
The surfaces that you created in the initial surfaces step were only partially ready to be aligned. In order to have a surface network that is ready to create a uniform mesh from, you need to detach the surfaces that were created across the boundaries or adjoining surfaces.

Detach Surfaces
The initial surfaces have to be separated into smaller regions that allow the boundaries of the adjacent surfaces to line up with each other.

Rebuild Surfaces
When a model made of different patches has uniform meshes, all surfaces have the same number and placement of isoparms as the surfaces next to them. If one surface has four subdivisions that are equally spaced throughout the surface, the adjacent surface has to have four subdivisions that are equally spaced throughout the surface. Figure 12 shows initial surfaces broken into smaller patch surfaces that have common boundaries with the adjacent patches. The surfaces have been rebuilt so all the surfaces have the same number of spans, and the isoparms all align.

[Figures 13 & 14] A simple texture map (top), shows the direction of the surfaces on a patch model (bottom).

Reverse Surfaces
By using a file-based texture map that defines the direction of UV parameterization, the surfaces that have been created can be reoriented so the UV coordinate space matches all surfaces, and the surfaces are facing the correct direction. Figure 13 shows a texture map that can be used to identify the direction of UV coordinates in a patch model. Figure 14 shows the surfaces of the model after the map has been applied. The goal is to get all of the surfaces to line up in a similar way and have the surface normals facing away from the model. This kind of texture map will show reversed surfaces quickly because the text will appear reversed. The U and V directions can also be quickly detected because the colors of the arrows indicate if the directions align between surfaces.

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