Offset Geometric Entities

This chapter summarizes, completes, and compares elementary curves, elementary surfaces, offset geometric entities, solid primitives, and form features. An elementary shape exists as an individual shape and has its own type, shape characteristics, and attributes. On the other hand, it is a segment or a structural element of a more complex shape and its characteristics and attributes probably depend on other elements in the complex shape. 

Application of reference geometric entities in assembly models is illustrated in Figure 8-23. The relationship of Part 1 and Part 2 cannot be expressed using any boundary geometric elements. Axis A, an element that is not integrated in the part boundary, allows definition of a uniaxiality relationship in the model. Full placement is realized by offset relationship Oy. Part 3 is positioned along axis A on Part 1 using surface S. The same possibility is not available in the case of Part 4. Reference plane Rp should be included in the model and referred to in coincidence assembly relationship. 

For the block example, a plane that is parallel to the top (or bottom) face of the base block was created first (by simply clicking more than three points on the surface). The plane is offset vertically to ensure a proper intersection between the sketch plane and the polygon mesh. The geometric entities obtained from the intersection are planar spline curves. The Auto Sketch capability of Rapidform can be used to extract a set of regular CAD-like line entities that best fit the spline curves. These standard line entities can be joined and parameterized by manually adding dimensions and constraints for a fully parameterized section profile, as shown in Fig. 18a. 

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