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270 6 Structural Pattern Recognition

for line segments lying in opposite directions. The following function satisfies this
requirement:

r I., --.* ,.

Figure 6.19. Three prototype tanks (toy models), labelled T1, T2 and T3, from left
to right.

Figure 6.20. Three views of prototype T1 taken at variable distance and
perspective angle, labelled T11, T12 and T13, from left to right.

The matching scores between prototypes TI vs. T2 and T1 vs. T3 are 59 and 57,
respectively. Table 6.3 shows the matching scores obtained for each of the
"unknown" patterns vs. the prototypes. In all cases, the unknown pattern is
correctly classified. It is clear, however, that the discrimination degrades with
increasing perspective angle.

Table 6.3. Matching scores between an "unknown" tank and each prototype. The
minimum always occurs for the prototype T1.