Topology & junctions
This page covers junction geometry (junction, pncJunction, area) and lane-junction stitching. The base lane topology fields live in Topology.
Two kinds of junction
| Type | Purpose | Editor entity |
|---|---|---|
junction | Physical intersection polygon | JunctionEntity |
pnc_junction | Planning & Control view of the junction | PNCJunctionEntity |
area | Generic region | AreaEntity |
Steps
1. Draw a junction polygon
ToolStrip → junction → drawPolygon. Click for vertices, double-click or Enter to close (polygonCanClose guard).
interface JunctionEntity {
id: string;
entityType: 'junction';
polygon: ApolloPolygon;
type?: 'UNKNOWN' | 'IN_ROAD' | 'CROSS_ROAD' | 'FORK_ROAD' | 'MAIN_SIDE' | 'DEAD_END';
overlapIds: string[];
}2. lane.junctionId derivation
Both central_curve endpoints are tested PIP against every junction.polygon. Both inside ⇒ lane.junctionId = junction.id. Half-inside lanes stay unassigned.
3. stitchLaneJunctions
src/core/geometry/laneJunctions.ts runs during cold-layer rebuild and pulls continuous end-start pairs to a shared miter point.
Start-start / End-end exclusion
isContinuousJunction(a, b) returns true only when a.isStart !== b.isStart. Start-start forks and end-end merges are excluded — pulling those boundaries to a shared miter point would corrupt the visible split/merge geometry (laneJunctions.ts:88-90).
4. PNC junction passage groups
interface PassageGroup {
id: string;
passages: Passage[];
}
interface Passage {
id: string;
signalIds: string[];
yieldIds: string[];
stopSignIds: string[];
laneIds: string[];
type: 'UNKNOWN_PASSAGE' | 'ENTRANCE' | 'EXIT';
}PNC junctions are higher-level than junction: each passageGroup represents a synchronised set of allowed lane sequences. The Inspector exposes add/remove controls for groups and passages (InspectorForms.tsx).
5. Overlap reconciliation
Derived ID convention: overlap_<sortedParticipantIds>. Participants get the overlap ID written into their own overlapIds. _userOverrides (overridePaths.ts) locks specific paths from being clobbered by future reconciles.
Options table
| Field | Type | Notes |
|---|---|---|
JunctionType | enum | UNKNOWN / IN_ROAD / CROSS_ROAD / FORK_ROAD / MAIN_SIDE / DEAD_END |
junction.polygon | ApolloPolygon | points: PointENU[] |
lane.junctionId | string | null | derived via PIP |
overlap.objects[].objectType | union | lane / signal / stopSign / crosswalk / junction / yieldSign / clearArea / speedBump / parkingSpace / pncJunction / rsu / area / barrierGate / unknown |
overlap.regionOverlaps[] | RegionOverlapInfo[] | region overlaps (lane↔crosswalk polygons) |
_userOverrides | string[] | locked paths (reconcile skips) |
pncJunction.passageGroups | PassageGroup[] | groups of passages by phase |
Shortcut cheatsheet
| Action | Key / Mouse | Notes |
|---|---|---|
| Draw junction | ToolStrip junction + click + dbl | drawPolygon |
| Draw PNC junction | ToolStrip pncJunction | drawPolygon |
| Bind lane to junction | drag endpoint into polygon | automatic PIP |
| Add passage | Inspector edit | pncJunction selected |
| Move polygon vertex | select junction → drag | editingPoint |
Troubleshooting
Half-in lane assigned wrongly
Won't happen — derivation requires both endpoints inside.
Stale junctionId after polygon move
Should trigger incremental reconcile; if stale, run a full reconcile.
Stitch broke a fork
isContinuousJunction should filter start-start pairs. Check laneJunctions.ts:88-90.
Overlap ID changes between import/export
ID generation is deterministic given sorted participant IDs. Check participant ID stability.
_userOverrides ignored
Path strings must match exactly (e.g. "objects.0.laneOverlapInfo.isMerge").
Source links
src/core/geometry/laneJunctions.tssrc/core/geometry/laneJunctions/internal.tssrc/core/elements/overlap/src/core/elements/overlap/overridePaths.tssrc/core/elements/derive/rules/src/components/layout/panels/InspectorForms.tsxsrc/types/apollo.ts:166-194(junction),:402-424(pncJunction),:347-398(overlap)
See also
Contributors
kent