This is the only classifier for parallel lines.

This is a complete list of the basic classifiers that are needed.

## 3.4 Basic Classifiers

Based on the primitive classifiers introduced in Sect. 3.3, we construct the *basic*

![0_image_0.png](0_image_0.png)

classifiers to determine the DRA relations in scenarios. For DRAf , we always need exactly four primitive classifiers to determine the relation. For DRAfp, in some cases we need an additional fifth classifier to determine the qualitative angle. We will first focus on the DRAf case. Given a qcc, we apply four basic classifiers three times: namely (1) to the first and second abstract dipole, (2) to the second and third and (3) to the first and third. Thus, we obtain an entry in the composition table. Consider a qcc with i = 1+ and a(SA) = ˆsAB,
a(SB) = ˆsAB and a(sC ) = SˆAC . Such a configuration has a realization as in Fig. 20. The dipole dX lies on the ray lX for X ∈ {*A, B, C*}. We now apply primitive classifiers to this scenario in the way defined in Section 2.1. Hence, we get the basic classifier for such a configuration:

| R(dpA, stB)   | =   | clis,s(dpA, stB)        |
|---------------|-----|-------------------------|
| R(dpA, edB)   | =   | clis,s(dpA, edB)        |
| R(dpB, stA)   | =   | com ◦ clis,s(dpB, stA)  |
| R(dpB, edA)   | =   | com ◦ clis,s(dpB, edA)  |
| R(dpB, stC )  | =   | clie,e(dpB, stC )       |
| R(dpB, edC )  | =   | clie,e(dpB, edC )       |
| R(dpC , stB)  | =   | com ◦ clie,e(dpC , stB) |
