Topology & Connections

Apollo lane topology defines three kinds of relationships between lanes:

Relationship	Apollo fields	Meaning
Successor / Predecessor	successor_id / predecessor_id	Lane B starts where lane A ends (longitudinal)
Left neighbor	left_neighbor_forward_lane_id	Adjacent lane to the left, same direction
Right neighbor	right_neighbor_forward_lane_id	Adjacent lane to the right, same direction

These relationships are what allow the routing module to plan paths across the map.

Connect successor / predecessor lanes

1. Select Connect Lanes mode from the toolbar (or press C)
2. Click the upstream lane (predecessor) — it highlights in orange
3. Click the downstream lane (successor) — the connection is created

The editor sets both directions:

• fromLane.successorIds gets toId added
• toLane.predecessorIds gets fromId added

Connected lanes are visualized as arrows in the connections layer.

Typical intersection pattern

    [approach lane] ──→ [turning lane] ──→ [exit lane]

The turning lane inside the junction gets predecessor = approach lane, successor = exit lane.

Set neighbor lanes

Neighbor relationships are set in the Properties panel of a selected lane.

Neighbor IDs are displayed as a read-only list. To add a neighbor:

1. Select the lane you want to set a neighbor on
2. In the Properties panel, click Add Left Neighbor or Add Right Neighbor
3. The editor enters neighbor-pick mode — click the adjacent lane
4. The relationship is set bidirectionally:
   • laneA.leftNeighborIds gets laneB
   • laneB.rightNeighborIds gets laneA

Remove connections

Select the lane in Select mode, then in the Properties panel click the × next to any ID in the predecessor/successor/neighbor lists.

removeElement also cleans up: deleting a lane removes all references to it from every other lane's predecessor, successor, and neighbor lists.

Junction assignment

When a lane's centerline midpoint falls inside a junction polygon, the export engine automatically sets lane.junction_id. You do not need to set this manually.

The routing map uses junction membership to set TopoNode.is_virtual:

is_virtual = lane is inside a junction
             AND has no left or right forward neighbors

Virtual nodes correspond to junction-internal connecting lanes that drivers cannot directly choose — the routing module treats them as zero-cost pass-throughs.

Road assignment

Lanes that share the same roadId property are grouped into one Road proto object at export time. You can set roadId in the Properties panel. Lanes without a roadId each become their own single-lane road section.

Viewing connections

Toggle the Connections layer in the layer panel (right side) to show or hide the directed-arrow overlay. Each arrow represents a successor relationship.

Connection arrows use a symbol layer with a chevron icon rotated to match the heading from the upstream lane end to the downstream lane start.