Expand description
map_model describes the world where simulations occur. Importing a map from OSM partly happens
in convert_osm and here.
Helpful terminology:
- ch = contraction hierarchy, for speeding up pathfinding
- degenerate intersection = only has 2 roads connected, so why is it an intersection at all?
- lc = lane-change (which is modelled very strangely: https://a-b-street.github.io/docs/tech/trafficsim/discrete_event/index.html#lane-changing)
- ltr = left-to-right, the order of lanes for a road
- osm = OpenStreetMap
Map objects are usually abbreviated in method names:
- a = area
- b = building
- tr = transit route
- ts = transit stop
- i = intersection
- l = lane
- pl = parking lot
- r = road
- ss = stop sign
- t = turn
- ts = traffic signal
Modules§
- city 🔒
- edits 🔒Once a Map exists, the player can edit it in the UI (producing
MapEditsin-memory), then save the changes to a file (asPermanentMapEdits). See https://a-b-street.github.io/docs/tech/map/edits.html. - make 🔒See https://a-b-street.github.io/docs/tech/map/importing/index.html for an overview. This module covers the RawMap->Map stage.
- map 🔒A bunch of (mostly read-only) queries on a Map.
- objects 🔒
- Useful utilities for working with OpenStreetMap.
- pathfind 🔒Everything related to pathfinding through a map for different types of agents.
Structs§
- A business located inside a building.
- Areas are just used for drawing.
- A building has connections to the road and sidewalk, may contain commercial amenities, and have off-street parking.
- A single city (like Seattle) can be broken down into multiple boundary polygons (udistrict, ballard, downtown, etc). The load map screen uses this struct to display the entire city.
- This is cheaper to store than a MovementID. It simply indexes into the list of movements.
- A traffic signal consists of a sequence of Stages that repeat in a cycle. Most Stages last for a fixed duration. During a single Stage, some movements are protected (can proceed with the highest priority), while others are permitted (have to yield before proceeding).
- A diagonal filter exists in an intersection. It’s defined by two roads (the order is arbitrary). When all of the intersection’s roads are sorted in clockwise order, this pair of roads splits the ordering into two groups. Turns in each group are still possible, but not across groups.
- Extra point-of-interest
- An intersection connects roads. Most have >2 roads and are controlled by stop signs or traffic signals. Roads that lead to the boundary of the map end at border intersections, with only that one road attached.
- This only applies to VehiclePathfinder; walking through these intersections is nothing special. And in fact, even lanes only for buses/bikes are ignored.
- A road segment is broken down into individual lanes, which have a LaneType.
- A lane is identified by its parent road and its position, ordered from the left.
- Represents changes to a map. Note this isn’t serializable – that’s what
PermanentMapEditsdoes. - A Movement groups all turns from one road to another, letting traffic signals and pathfinding operate at a higher level of abstraction.
- A movement is like a turn, but with less detail – it identifies a movement from one directed road to another. One road usually has 4 crosswalks, each a singleton Movement. We need all of the information here to keep each crosswalk separate.
- None corresponds to the native name
- Refers to a road segment between two nodes, using OSM IDs. Note OSM IDs are not stable over time and the relationship between a road/intersection and way/node isn’t 1:1 at all.
- Parking lots have some fixed capacity for cars, and are connected to a sidewalk and road.
- A path between two endpoints for a particular mode. This representation is immutable and doesn’t prescribe specific lanes and turns to follow.
- For callers needing to request paths with a variety of RoutingParams. The caller is in charge of the lifetime, so they can clear it out when appropriate.
- MapEdits are converted to this before serializing. Referencing things like LaneID in a Map won’t work if the basemap is rebuilt from new OSM data, so instead we use stabler OSM IDs that’re less likely to change.
- Represents a specific point some distance along a lane.
- Options for converting RawMaps to Maps.
- A Road represents a segment between exactly two Intersections. It contains Lanes as children.
- A filter placed somewhere along a road
- Tuneable parameters for all types of routing.
- A Turn leads from the end of one Lane to the start of another. (Except for pedestrians; sidewalks are bidirectional.)
- Turns are uniquely identified by their (src, dst) lanes and their parent intersection. Intersection is needed to distinguish crosswalks that exist at two ends of a sidewalk.
- A contiguous set of roads with access restrictions. This is derived from all the map’s roads and kept cached for performance.
Enums§
- Businesses are categorized into one of these types.
- Classifies pedestrian and cyclist crossings. Note lots of detail is missing.
- The type of a modal filter. Most of these don’t have semantics yet; the variation is just for visual representation
- The kind of traffic control present at an intersection.
- What kind of feature an
Intersectionactually represents. Any connection between roads in the network graph is represented by anIntersection, but many of them are not traffic “intersections” in the common sense. - Represent no parking as Private(0, false).
- Who’s asking for a path?
- One step along a path.
- When pathfinding with different
RoutingParamsis done, a temporary pathfinder must be created. This specifies what type of pathfinder and whether to cache it. - See https://wiki.openstreetmap.org/wiki/Forward_%26_backward,left%26_right.
- Either a lane or a turn, where most movement happens.
Constants§
- From some manually audited cases in Seattle, the length of parallel street parking spots is a bit different than the length in parking lots, so set a different value here.