geo/laneGeometry

Lane boundary computation, width sampling, and heading calculations using @turf/turf.

computeBoundaries

function computeBoundaries(
  centerLine: Feature<LineString>,
  widthMeters: number
): {
  left: Feature<LineString>
  right: Feature<LineString>
}

Computes left and right boundary lines by offsetting the centerline by ±widthMeters/2.

Uses turf.lineOffset(centerLine, distance, { units: 'meters' }).

Parameters

Name	Type	Description
centerLine	Feature<LineString>	Lane centerline in WGS84
widthMeters	number	Full lane width in meters

Example

const { left, right } = computeBoundaries(lane.centerLine, lane.width)
// left and right are LineString features parallel to centerLine

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computeLaneSamples

function computeLaneSamples(
  centerLine: Feature<LineString>,
  halfWidthMeters: number
): LaneSampleAssociation[]

Returns a LaneSampleAssociation[] sampled every 1 m along the centerline. Each sample stores { s, width } where s is the arc-length position and width is halfWidthMeters (constant for uniform-width lanes).

Used to populate ApolloLane.left_sample and right_sample.

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sampleLineEveryMeter

function sampleLineEveryMeter(line: Feature<LineString>): Array<[number, number]>

Returns an array of [lng, lat] coordinates sampled every 1 m along the line using turf.along. Includes the start and end points.

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computeStartHeading

function computeStartHeading(centerLine: Feature<LineString>): number

Returns the bearing (degrees, 0 = north, clockwise) from the first to the second coordinate of the centerline. Used to set CurveSegment.heading in the exported proto.

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buildLanePolygon

function buildLanePolygon(left: Feature<LineString>, right: Feature<LineString>): Feature<Polygon>

Constructs a filled polygon from left and right boundary lines. The polygon is formed by:

1. Left boundary coordinates (start → end)
2. Right boundary coordinates (end → start, reversed)
3. Closing back to the left boundary start

Used by MapEditor to render the lane fill layer.

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laneMidpointInfo

function laneMidpointInfo(line: Feature<LineString>): { point: Feature<Point>; bearing: number }

Returns the midpoint of the line and the bearing at that point. Used by MapEditor to position and orient direction-arrow symbols.

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pointToS

function pointToS(line: Feature<LineString>, point: Feature<Point>): number

Returns the arc-length s (meters from start) of the nearest point on line to point. Wraps turf.nearestPointOnLine(line, point).properties.location * turf.length(line).

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lineEndpoints

function lineEndpoints(line: Feature<LineString>): {
  start: [number, number]
  end: [number, number]
}

Returns the first and last coordinates of a LineString feature.