Lane Topology Layer
The lane-topology layer contains the lane group, lane group connector, lane and lane connector topology of the lane model. It also contains a simplified 2D boundary geometry of the lane model, which is used to determine tile affinity and overflow.
The LaneTopologyLayerTile is top-level message for the lane-topology layer tiles. It contains the definitions of the lane groups and lane group connectors that live in this tile, as well as references to the lane groups that intersect this tile.
Lane Topology Inclusion Rules:
- Lane group connectors whose first geometry point fall in the tile.
- Lane groups whose start lane group connector fall in the tile, per above.
- Lane group connector intersection references for lane groups whose boundary geometry or lane group connector boundary geometry intersect the tile.
Lane group connectors are defined by an ID and the list of lane groups that connect at them. They include a 2D linear boundary geometry.
A lane group is defined by an ID, references to their start and end lane group connectors, and the list of lanes they contain.
By definition, the start lane group connector must be in the same tile as the lane group, so it only needs a local reference ID. The end lane group connector may be in a different tile, so must be a tile ID. Even when the end lane group connector happens to be in the current tile, the tile ID of the end lane group connector will be provided for consistency.
Lane groups contain the list of tiles their boundary geometry intersects (including the current tile). This information is used in conjunction with intersecting_lane_group_refs in the top-level LaneTopologyLayerTile message to ease overall resolution of lane group overflows.
LineString2dOffset is used to encode 2D polylines for lane group boundary geometry and lane group connector boundary geometry.
The representation of an individual lane topology is very lightweight. It is defined by the paring of its start and end ordinal lane connector numbers on the lane group connector.