Page 118 - DCAP504_Computer Graphics

Unit 8: 3-D in Computer Graphics

The separate listing of vertices, edges and polygons prove to be a very convenient method to refer to
individual polygonal components. The object can be displayed efficiently by using the information
extracted from the edge table and drawing the component lines. In some cases only tables are used, i.e.
the vertex and polygon table.
The table 8.2 depicts the geometric data representation for the two adjacent polygon surfaces that are
shown in the figure 8.5.

Figure 8.5 : Adjacent Polygon Surface

Table 8.2 : Vertex, Edge and Polygon Surface Tables

Vertex Table
V1: x1,y1,z1
V2: x2,y2,z2
V3: x3,y3,z3
V4: x4,y4,z4
V5: x5,y5,z5

Edge table
E1:V1,V2
E2:V2,V3
E3:V1,V3
E4:V3,V4
E5:V4,V5
E6:V1.,V5

Polygon surface
table
S1: E1,E2,E3
S2:E3,E4,E5,E6

The data tables that are written for the polygons can be tested for their consistency by undergoing the
following tests. The tests check whether,
1. Each vertex is listed as an endpoint for at least 2 edges.
2. Each edge is part of at least one polygon.
3. Each polygon is closed.
4. Each polygon has a minimum of one common edge.

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