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src/Event.js

@@ -1,14 +1,15 @@
 
 export default class Event {
 
-    constructor (p, featureId, ringId, eventId) {
+    constructor (p, featureId, ringId, eventId, vertexId) {
         this.p = {
             x: p[0],
             y: p[1]
         }
         this.featureId = featureId
         this.ringId = ringId
         this.eventId = eventId
+        this.vertexId = vertexId
 
         this.otherEvent = null
         this.isLeftEndpoint = null

src/Segment.js

@@ -1,7 +1,16 @@
 export default class Segment {
 
-    constructor (event) {
+    constructor (event, segmentId) {
         this.leftSweepEvent = event
         this.rightSweepEvent = event.otherEvent
+        this.segmentId = segmentId
+    }
+
+    get earliestVertexId () {
+        return Math.min(this.leftSweepEvent.vertexId, this.rightSweepEvent.vertexId)
+    }
+
+    get isPartOfOuterRing () {
+        return this.leftSweepEvent.ringId === 0
     }
 }

src/fillQueue.js

@@ -5,17 +5,16 @@ export default function fillEventQueue (geojson, eventQueue) {
     if (geojson.type === 'FeatureCollection') {
         const features = geojson.features
         for (let i = 0; i < features.length; i++) {
-            processFeature(features[i], eventQueue)
+            processFeature(features[i], eventQueue, i)
         }
     } else {
-        processFeature(geojson, eventQueue)
+        processFeature(geojson, eventQueue, 0)
     }
 }
 
-let featureId = 0
-let ringId = 0
-let eventId = 0
-function processFeature (featureOrGeometry, eventQueue) {
+function processFeature (featureOrGeometry, eventQueue, featureId) {
+    let eventId = 0
+
     const geom = featureOrGeometry.type === 'Feature' ? featureOrGeometry.geometry : featureOrGeometry
     let coords = geom.coordinates
     // standardise the input
@@ -26,12 +25,11 @@ function processFeature (featureOrGeometry, eventQueue) {
         for (let ii = 0; ii < coords[i].length; ii++) {
             let currentP = coords[i][ii][0]
             let nextP = null
-            ringId = ringId + 1
             for (let iii = 0; iii < coords[i][ii].length - 1; iii++) {
                 nextP = coords[i][ii][iii + 1]
 
-                const e1 = new Event(currentP, featureId, ringId, eventId)
-                const e2 = new Event(nextP, featureId, ringId, eventId + 1)
+                const e1 = new Event(currentP, featureId, ii, eventId, iii)
+                const e2 = new Event(nextP, featureId, ii, eventId + 1, iii + 1)
 
                 e1.otherEvent = e2
                 e2.otherEvent = e1
@@ -51,5 +49,4 @@ function processFeature (featureOrGeometry, eventQueue) {
             }
         }
     }
-    featureId = featureId + 1
 }

src/runCheck.js

@@ -10,12 +10,13 @@ export default function runCheck (eventQueue, ignoreSelfIntersections) {
 
     const intersectionPoints = []
     const outQueue = new TinyQueue([], checkWhichSegmentHasRightEndpointFirst)
-
+    let segmentId = 0
     while (eventQueue.length) {
         const event = eventQueue.pop()
         if (event.isLeftEndpoint) {
             // debugEventAndSegments(event.p, outQueue.data)
-            const segment = new Segment(event)
+            const segment = new Segment(event, segmentId)
+            segmentId = segmentId + 1
             for (let i = 0; i < outQueue.data.length; i++) {
                 const otherSeg = outQueue.data[i]
                 if (ignoreSelfIntersections) {

src/utils.js

@@ -1,3 +1,5 @@
+import {orient2d} from 'robust-predicates'
+
 export function testSegmentIntersect (seg1, seg2) {
     if (seg1 === null || seg2 === null) return false
 
@@ -17,6 +19,12 @@ export function testSegmentIntersect (seg1, seg2) {
     const x4 = seg2.rightSweepEvent.p.x
     const y4 = seg2.rightSweepEvent.p.y
 
+    const score1 = orient2d(x1, y1, x2, y2, x3, y3)
+    const score2 = orient2d(x1, y1, x2, y2, x4, y4)
+    if (score1 === score2) {
+        return false
+    }
+
     const denom = ((y4 - y3) * (x2 - x1)) - ((x4 - x3) * (y2 - y1))
     const numeA = ((x4 - x3) * (y1 - y3)) - ((y4 - y3) * (x1 - x3))
     const numeB = ((x2 - x1) * (y1 - y3)) - ((y2 - y1) * (x1 - x3))
@@ -32,7 +40,24 @@ export function testSegmentIntersect (seg1, seg2) {
     if (uA >= 0 && uA <= 1 && uB >= 0 && uB <= 1) {
         const x = x1 + (uA * (x2 - x1))
         const y = y1 + (uA * (y2 - y1))
-        return [x, y]
+
+        const seg1Start = seg1.leftSweepEvent.vertexId < seg1.rightSweepEvent.vertexId ? seg1.leftSweepEvent : seg1.rightSweepEvent
+        const seg2Start = seg2.leftSweepEvent.vertexId < seg2.rightSweepEvent.vertexId ? seg2.leftSweepEvent : seg2.rightSweepEvent
+        return {
+            seg1,
+            seg2,
+            intersection: [x, y],
+            distanceFromSeg1Start: distance([seg1Start.p.x, seg1Start.p.y], [x, y]),
+            distanceFromSeg2Start: distance([seg2Start.p.x, seg2Start.p.y], [x, y])
+        }
     }
     return false
 }
+
+function distance (p1, p2) {
+    let xs = p2[0] - p1[0]
+    let ys = p2[1] - p1[1]
+    xs *= xs
+    ys *= ys
+    return Math.sqrt(xs + ys)
+}

test/test.e2e.js

@@ -42,5 +42,5 @@ test('ignoreSelfIntersections param works', (t) => {
 
     const intersections = sweepline(geojson, false)
     t.is(intersections.length, 3)
-    t.deepEqual(intersections[0], [19.88085507071179, -9.98118374351003])
+    t.deepEqual(intersections[0].intersection, [19.88085507071179, -9.98118374351003])
 })