Refined Route Instructions

The theoretical framework for the refinement of route instructions derived in this paper can be applied for various types of guidance systems. In the following sections we describe the principle of refining routes instructions based on the example of a GPS-based tour guiding system. The range of applications, however, is not limited to this example, but applies for all route guiding systems that exhibit some degree of uncertainty.

Application example: A GPS-based tour guide

Let’s assume a predefined list of waypoints that describes a sightseeing tour and leads tourists through a region containing a set of attractions alike Figure 1. The waypoints define a route that passes by the attractions, while the circles around the waypoints represent the accuracy of the waypoint’s position. Alternatively, these circles could indicate the region within which the guiding system may provide simple instructions to the tourist, without the risk of misleading the tourist. The instructions are provided by the means of a GPS-based guiding device that uses arrows as instructions. Specifi-cally, the guiding system uses straight arrows as unrefined instructions and bent ar-rows as refined instruction (Figure 6). Directional change is derived from the prede-fined route for each waypoint and indicated by adjusting the arrow showing the con-secutive way accordingly.

A bent arrow is used when a wayfinder is approaching a waypoint. In this situation, the tip of the arrow is already pointing towards the next waypoint, while the end of the arrow is still pointing towards the upcoming waypoint. This visual instruction represents the situation in the real world closer than an unrefined instruction, i.e., “go straight and then turn right”.

Figure 6. A wayfinder w navigating between waypoint a and b by following the instruction i. (a) A straight arrow is used for an unrefined instruction. This representation is mapped to the stage of closeness 1. (b) Refined routing instructions that map to the stages of closeness 2 to 5. (c) The stages of closeness 6 to 8 show again a straight arrow.

The guiding system continuously updates the navigator’s position and accuracy, determines the type of relation between navigator and waypoints, and adjusts the display accordingly. The adjustment of the display is based on a lookup table that maps the spatial configuration between navigator and waypoint to the corresponding representation on the screen. An example of such a mapping is shown in Figure 6. The mapping between the stages of closeness and the visual instructions can be ad-justed for each route. For example, the visual instruction in Figure 6b could not be shown until the stage of closeness 4. This shift guides the wayfinder more closely along the route. On the other hand, mapping the stage of closeness 4 to Figure 6c gives a wayfinder more freedom in following a route.

Discussion

Guiding systems typically use the distance between wayfinder and waypoint as lead-ing criteria. Based on these factors, the position for the next instructions is calculated and the instruction generated. This approach works well for network-based navigation (i.e., streets, etc.), because the positional uncertainty of the wayfinder is compensated by the clear definition of the road segments that can be followed, and by distinct way-points, i.e., intersections of the street network. For routes that do not exhibit such structures, however, the instructions need to be refined. In the approach presented in this paper, we base this refinement on topological stages of closeness. The main bene-fit of this approach is that it considers positional uncertainty when determining the next instruction.

Another benefit of the approach is the higher granularity (8 stages of closeness) of potential route instructions. From a topological point of view, the traditional approach uses a CSEP for the waypoint (position and radial distance) and a point to derive the instructions, which limits the number of stages of closeness to 4 (i.e., the number of possible topological relations between a point and a CSEP). Instead of treating the position of the wayfinder as a simple point, we base our model on a CSEP. This ap-proach increases the number of possible stages of closeness to 8, which results in higher granularity of possible route instructions (independent of the representation of the instructions) and finally increased accuracy and reliability of the guiding system.