Announce when the route changes due to changes in the traffic situation

[mvglasow]

When an active route changes due to changes in the traffic situation, the user is currently not made aware of this.

If the change affects the next maneuver (i.e. the user is diverted off the current road), the user may miss the maneuver for that reason.

Also, users are mot made aware that their ETA has suddenly changed.

We want to trigger some action when the route changes, e.g. a spoken announcements or an OSD icon appearing.

Challenge 1: Detection of such changes. Maybe this can be done when the route path is refreshed: if route path segments change, it means the route has changed and the event should fire.

Challenge 2: Implementation of an event which can trigger the desired actions. AFAIK we don’t currently have events, only attributes which can trigger actions on update.

[mvglasow]

We also need to think about UX for these cases:

• Should we notify the user if the original route calculation is already avoiding some roads because of the traffic situation (i.e. the first calculated route is different from what would get chosen, were it not for the traffic)? And how would we know this is the case?
• Should we notify the user if an already calculated route changes because of traffic changes? (Presumably yes) And should we mention whether this is due an improved traffic situation, or due to a worsened one?
• How should we notify the user? Spoken announcement? Or a visual element (e.g. OSD)? In the latter case, should it remain in the display all the time, or just until the user clears it?

[mvglasow]

Maybe this could be incorporated into a general traffic status display which indicates:

• Is a traffic provider active and (capable of) delivering messages?
• Are active messages present?
• Do they affect our route?
• Are we avoiding them?

For example, a traffic jam symbol indicates general status:

• The icon is filled when messages are active, else it changes to an outline.
• An overlay in the bottom-right corner is shown when no service is active, or when the active service cannot pick up any messages (e.g. because the service is TMC and we are not in a TMC reception area, or the service is Internet-based and we have no data connection). When multiple services are configured, an exclamation mark indicates that some services are available while others are not; a cross indicates no sources are available.
• A detour icon in another corner (or next to the icon) shows we have been rerouted around a traffic distortion.
• TODO: another icon (shown instead of the detour icon) to indicate we are encountering an unavoidable traffic distortion on the route.

If spoken announcements are enabled, speak an announcement whenever the route changes due to the traffic situation. This includes all cases in which the detour icon appears or disappears, but includes other cases as well (e.g. a second traffic distortion has just been reported and bypassed).

The visual indication could be an OSD similar to navigation_status. Announcements could borrow from maneuver announcements.

The remaining challenge now is to detect route changes (and, optionally, what change it is: deviating from the main route, returning to the main route, or something else).

[mvglasow]

An approach to route changes could be to compare the added and removed segments to the navigation map (before and after rerouting)—if a segment is on the navigation map, it is part of the route:

• If a new traffic distortion (or cost increase) refers to a segment on the old route, it at least increases the ETA. If it is only on the old route but not on the new one, it means we have avoided a traffic distortion.
• If a removed traffic distortion (or cost decrease) refers to a segment which is not on the old route but on the new route, it means we are no longer avoiding a traffic distortion. If it is on both the old and the new route, it decreases the ETA.

If the first route created already avoids traffic distortions, we will not have a way of detecting that as a detour, unless we ignore traffic for the first calculation and then immediately trigger a recalculation.

Another difficulty is dealing with lesser evils, i.e. the cheapest way to avoid a huge traffic jam is through a smaller one. Should we report that as a detour or as a traffic jam ahead?