e-Profiles, Spring 2002: Pro/ANATOMY--Modeling Body Parts in Pro/ENGINEER®

Key Principles for Anatomical Surface Modeling

Now that you know what tools to use, here are some things to keep in mind as you build your anatomical surface model. Consider these principles as we walk through the process of modeling a human finger.

1. Build a good skeleton part. For our finger modeling exercise, take this advice literally. This means defining all of your key shape and motion information in the skeleton before you even think about what the surface needs to look like. Figure 5 shows a simple skeleton of our finger model, consisting of a sketched datum curve with three line segments aligned to the default coordinate system.

Figure 5.

2. Plan your datum curve framework well. Think where the boundaries for your SBBs will be and how to connect them to one another. The key to a smooth, contiguous surface is how well you plan your framework. You may want to first create revolved surfaces over the skeleton segments (Fig. 6) to help visualize how the surfaces need to come together and follow the motion of the skeleton.

3. Construct a simple datum curve framework. Tie your framework to the skeleton and run it through the motions. The surface will only hold up if the framework remains intact. In Figure 7, datum curves representing the cross-section of our finger are added at the vertices of the skeleton segments. Since we want the finger to bend, we need to write a relationship to keep these curves at the correct angle relative to the skeleton.



Figure 6.	Figure 7.	Figure 8.

4. Build a simple surface by boundaries. Check out how the surface looks and how much more framework you need to hold it up the way you want. See how it responds to skeleton manipulation. The surface in Figure 8 shows that we need more control to get the desired shape.

5. Limit the number of segments in your surface. The fewer segments the better. Too many segments cause problems later when knitting boundaries together. Reduce the number by adding more approximate composite curves, and by using control points in your SBB. By adding control points (Fig. 9), we can pull the kinks out of our finger. This reveals that we need additional datum curves to round the fingertip and shape the sides (Fig. 10).



Figure 9.		Figure 10.

6. Get all or most of your surfaces under one SBB. Anatomical surfaces are tangent to one another and have no orthogonal references for controlling unsupported surface boundaries. It will therefore be difficult to get all subsequent SBBs tangent to one another if you plan to patch your surfaces together. Once we achieve our desired shape, we can go in and add other features like fingernails and creases (Fig. 11).

Figure 11.