How / when to trigger "navigation texts"?

[Bernd Welter]

Hi there,

one of my partners uses PTV Developer Routing API to calculate routes including maneuver events:

On the one hand he wants to visualize dedicated icons in the map that show the user what kind of maneuver is expected at a specidif location. That can be done via

• the coordinates
• the type
• the relative direction

Checked.

But as he also wants to create some online navigation based on the API hw wonders when to inform the user about some

• in 200 meters turn left
• in the roundabout take the 3rd exit

and so he needs to know when it is time to trigger this. My spontaneous approach was to calculate some geofence:

500m isochrone / area of reach around the event

Would be relevant to know the underlying road network because there's a difference between

• leaving a highways (I prefer that info 1-2km in advance)
• leaving an urban road (probably a smaller horizon is sufficient)

Any recommendations or experiences you want to share with us?

Bernd

[Bernd Welter]

If the routing is recalculated every few seconds based on the current (x,y) and the destination (x,y) the DistanceFromStart of maneuvers can be used to decide about triggering event infos

[Michael.Hubschneider]

Generating maneuver hints might be not as easy as it looks, here are some hints:

• Maneuver hints are generally generated depending on the time you need to arrive at the next maneuver point. The higher the speed, and the bigger the roads you are on or you go to, the earlier the hints.
• Typically there are two announcements, the early announcement and the "now" announcement.
• The moment of the hints also depends on units, e.g. early motorway hints in Germany may be one km ahead. They are in the US 1 mile ahead and always should be in local units (e.g. 1/4 mile, 300 yards).
• You may be missing information you need for more sophisticated announcements, e.g., you want to wait to make the "now turn right" announcement until the last opportunity to turn right too early has passed.
• Different vehicles have different speeds, so this may cause completely different moments for the announcement, if you have bicyclists or even pedestrians

[Maximilian Vogel]

If the routing is recalculated every few seconds based on the current (x,y) and the destination (x,y) the DistanceFromStart of maneuvers can be used to decide about triggering event infos

I think it shouldn't be necessary to recalculate the route every few seconds. Instead, I suggest to process the polyline. You can calculate the distance for each polyline segment. The coordinates of the maneuver events should be present in the polyline (at least for the geojson format; otherwise you need to find the closest polyline coordinate for the event coordiante). So you can then calculate the distance from each polyline coordinate to the next event by summing up the distances until the next event. And then you can just "move" the vehicle's position along the polyline and calculate the remaining distance to the next event.
Furthermore, you could trigger a re-calculation of the route if the vehicle's position is too far away from the polyline or the current segment of the polyline due to a missed exit or because of a wrong exit was taken.