Expose continuous distance crossed for vehicles. #392

headless/src/main.rs

@@ -386,10 +386,13 @@ struct AgentPosition {
     /// The distance crossed so far by the agent, in meters. There are some caveats to this value:
     /// - The distance along driveways between buildings/parking lots and the road doesn't count
     ///   here.
-    /// - The distance will not change while an agent is travelling along a lane; it'll only
-    ///   increment when they completely cross one step of their path.
     /// - The distance only represents the current leg of the trip. If somebody walks to a car, the
     ///   distance will reset when they begin driving, and also vehicle_type will change.
+    /// - No meaning for bus passengers currently.
+    /// - For buses and trains, the value will reset every time the vehicle reaches the next
+    ///   transit stop.
+    /// - The value might be slightly undercounted or overcounted if the path crosses into or out
+    ///   of an access-restricted or capped zone.
     distance_crossed: Distance,
     /// None for buses
     person: Option<PersonID>,

sim/src/mechanics/driving.rs

@@ -1017,11 +1017,21 @@ impl DrivingSimState {
         let path = car.router.get_path();
         let time_spent_waiting = car.state.time_spent_waiting(now);
 
+        // In all cases, we can figure out exactly where we are along the current queue, then
+        // assume we've travelled from the start of that, unless it's the very first step.
+        let front = self.get_car_front(now, car);
+        let current_state_dist =
+            if car.router.head() == Traversable::Lane(path.get_req().start.lane()) {
+                front - path.get_req().start.dist_along()
+            } else {
+                front
+            };
+
         AgentProperties {
             total_time: now - car.started_at,
             waiting_here: time_spent_waiting,
             total_waiting: car.total_blocked_time + time_spent_waiting,
-            dist_crossed: path.crossed_so_far(),
+            dist_crossed: path.crossed_so_far() + current_state_dist,
             total_dist: path.total_length(),
         }
     }
@@ -1045,12 +1055,7 @@ impl DrivingSimState {
         dist_ahead: Option<Distance>,
     ) -> Option<PolyLine> {
         let car = self.cars.get(&id)?;
-        let front = self.queues[&car.router.head()]
-            .get_car_positions(now, &self.cars, &self.queues)
-            .into_iter()
-            .find(|(c, _)| *c == id)
-            .unwrap()
-            .1;
+        let front = self.get_car_front(now, car);
         car.router.get_path().trace(map, front, dist_ahead)
     }
 
@@ -1161,6 +1166,15 @@ impl DrivingSimState {
         intersections.populate_blocked_by(now, &mut graph, map, &self.cars, &self.queues);
         graph
     }
+
+    fn get_car_front(&self, now: Time, car: &Car) -> Distance {
+        self.queues[&car.router.head()]
+            .get_car_positions(now, &self.cars, &self.queues)
+            .into_iter()
+            .find(|(c, _)| *c == car.vehicle.id)
+            .unwrap()
+            .1
+    }
 }
 
 impl IndexableKey for CarID {