SDK for iOS Developer's Guide

Signpost Parsing

This section provides guidelines on how to use HERE Mobile SDK Signpost object to present visual maneuver instructions which match the audible voice instructions during turn-by-turn guidance. While the high-level guidelines in this section are applicable to both HERE Android and iOS SDKs, the detailed descriptions are generic and do refer to the specific APIs available on either platform.

Signs represent textual and graphic information posted along roads. The information is always represented as text, but may originate from a graphical icon. Signpost information may be used for route guidance (both audible and visual guidance) and map display. A navigation system may prefer using the signpost text rather than the street/ramp name as the latter may not always match what is on the sign in reality and may confuse a user. The signpost feature supports the user navigating through complex situations and provides a conformation for a maneuver by presenting the same direction information as shown on the street signs in reality.

Signpost Content

The Signpost representation is an association between two links, the "From link" and the "To link". They are not necessarily contiguous. The "From link" is the link prior to a maneuver decision point. A maneuver decision is a point where the road splits and the driver is unable to determine the direction to traverse. The "To link" is the link traversed after the decision point.

Note: Not all maneuvers contain Signpost information.
Based on the map attributes, HERE Mobile SDKs aggregate the following information into a Signpost object:
  • Exit number
  • Exit text
  • Exit icon
  • Exit directions
  • Foreground / Background color
Exit directions is an array of information shown on the sign and can contain the following information:
  • Language i.e. the three letter MARC code for the label language
  • Route direction
  • Route name
  • Text representing auxiliary information. Typically the auxiliary information contains a destination name such as a city or a characteristic place (such as "airport")
Each index in the exit directions array will typically contain only one of Route direction, Route name and Text. Since the origin data is not always consistent, it is advisable to concatenate the route name and route direction fields.

Parsing Basic Signpost Information

To present an audible or visual maneuver instruction, information from the Maneuver and Signpost objects can be combined as shown in the figure below:

Figure 1. Parsing for audible instructions for a basic sign

Not all exit direction information presented on the real signpost might be relevant to the user’s route. To avoid a flood of information, which easily could lead to confusion, especially for the voice output, exit directions information which is irrelevant for a driver’s route may be suppressed.

To achieve this, the signpost information of the next maneuver and the next-next maneuver can be compared and only the exit direction information valid for both maneuvers may be presented for the next maneuver. An example of this is shown in the figure below.

Figure 2. Filtering out exit directions information

There may be some cases where there is no matching exit direction information in the next maneuver and the next-next maneuver. In this case the recommendation is to present the first index in the exit directions array of the next maneuver.