Computer Aided Engineering Design

258 COMPUTER AIDED ENGINEERING DESIGN

Figure 8.14 Data tables for a tetrahedron wireframe

4

1

3

2

(1)

(3)

(4)

(5)

(6)

(2)

z

x y

Edge table

Edge Number Vertex 1 Vertex 2

112

223

313

414

534

624

Vertex table

Vertex xyz

Number

1000

2140

3–320

4–124

Figure 8.15 Wireframe (left) that may represent two solids on the right

While data structures used in wireframe models are simple, wireframes are nonunique and ambiguous,
which is because the models do not include the facet information. Consider a wireframe in Figure
8.15 left which can either represent a solid on top right or bottom right.

Another example is a block void within a block (Figure 8.16). While we understand that each
quadrilateral (or a square) represents a (flat) face, the opening of the void is not quite discernable and
the wireframe can represent any of the three possibilities shown below. Note that the three objects
would be identical only for a regular cubic void within a cube.