Crosswalk Lane Traversal
In most cases a Crosswalk defines a simple rectangular path normal to the Road Segment it crosses. This, however, is only one of many possibilities. Sometimes a Crosswalk moves at a diagonal as shown:
And the shape can be irregular to allow for convenient pedestrian access:
To handle irregular geometries, we concern ourselves only with two straight lines for each Lane traversed by a Crosswalk normal to the Lane for the approach into and exit from the Crosswalk.
We rely on a Symbology domain to interpret the painted markings (or other information) and provide the corresponding Approach and Exit distances for an interpreted Crosswalk.
- Crosswalk + Inside division + Outside division + Road segment
Note that Road segment must be the same as Lane.Road segment with the further constraint that this value must match either the associated Crosswalk’s Inner or Outer road segment.
This is a line normal to the Lane and the same width as the Lane on one side of the Crosswalk. If the Crosswalk is in front of the Ego Vehicle relative to its current heading, the line closest to the Ego Vehicle is the approach and the line on the other side of the Crosswalk is the Exit Line.
If there is a legal turn up ahead of the Ego Vehicle, the first line that the Ego Vehicle would encounter if it took the turn becomes the approach.
For Crosswalks behind the Ego Vehicle, the exit Line will be the one that the Ego Vehicle would have passed last had it taken a route through that Crosswalk. The choice can be arbitrary for any Crosswalk behind the Ego Vehicle, but must be correct for any Crosswalk ahead.
In fact, there is really no need to track Crosswalks that are not in front of the driving direction (forward or reverse) of the Ego Vehicle.
When the Ego Vehicle makes a U-turn, the approach and exit line roles reverse. So approaches become exists and vice versa.
Type: Distance Ahead
See the description for the Approach line
Type: Distance Ahead